diff --git a/backend/src/Health.Infrastructure/Services/bce_signer.cs b/backend/src/Health.Infrastructure/Services/bce_signer.cs
new file mode 100644
index 0000000..d30d4a1
--- /dev/null
+++ b/backend/src/Health.Infrastructure/Services/bce_signer.cs
@@ -0,0 +1,49 @@
+using System.Globalization;
+using System.Security.Cryptography;
+
+namespace Health.Infrastructure.Services;
+
+/// <summary>
+/// 百度云 BCE v1 签名算法（与 baidubce-sdk 算法一致）
+/// </summary>
+public static class BceSigner
+{
+    private const int ExpirySeconds = 1800;
+    private const string SignedHeaders = "content-length;content-type;host;x-bce-date";
+
+    public static string BuildAuthorization(
+        string accessKeyId,
+        string secretAccessKey,
+        string method,
+        string path,
+        string host,
+        DateTime utcNow,
+        int contentLength,
+        string contentType)
+    {
+        var timestamp = utcNow.ToString("yyyy-MM-ddTHH:mm:ss'Z'", CultureInfo.InvariantCulture);
+
+        var canonicalHeaders = string.Join("\n",
+            $"content-length:{contentLength}",
+            $"content-type:{Normalize(contentType)}",
+            $"host:{Normalize(host)}",
+            $"x-bce-date:{Normalize(timestamp)}");
+
+        var canonicalRequest = $"{method}\n{path}\n\n{canonicalHeaders}";
+        var authStringPrefix = $"bce-auth-v1/{accessKeyId}/{timestamp}/{ExpirySeconds}";
+
+        var signingKeyDigest = HMACSHA256.HashData(
+            Encoding.UTF8.GetBytes(secretAccessKey),
+            Encoding.UTF8.GetBytes(authStringPrefix));
+        var signingKeyHex = Convert.ToHexString(signingKeyDigest).ToLowerInvariant();
+
+        var signature = HMACSHA256.HashData(
+            Encoding.UTF8.GetBytes(signingKeyHex),
+            Encoding.UTF8.GetBytes(canonicalRequest));
+        var signatureHex = Convert.ToHexString(signature).ToLowerInvariant();
+
+        return $"{authStringPrefix}/{SignedHeaders}/{signatureHex}";
+    }
+
+    private static string Normalize(string s) => Uri.EscapeDataString(s);
+}
diff --git a/backend/src/Health.Infrastructure/Services/bce_sms_client.cs b/backend/src/Health.Infrastructure/Services/bce_sms_client.cs
new file mode 100644
index 0000000..cd90e12
--- /dev/null
+++ b/backend/src/Health.Infrastructure/Services/bce_sms_client.cs
@@ -0,0 +1,64 @@
+using System.Globalization;
+using Microsoft.Extensions.Configuration;
+using Microsoft.Extensions.Logging;
+
+namespace Health.Infrastructure.Services;
+
+/// <summary>
+/// 百度云 SMS v3 短信发送客户端（HttpClient 直连 + BCE v1 签名）
+/// </summary>
+public sealed class BceSmsClient(HttpClient http, IConfiguration cfg, ILogger<BceSmsClient> log)
+{
+    private const string Path = "/api/v3/sendSms";
+    private const string ContentType = "application/json; charset=utf-8";
+
+    private readonly HttpClient _http = http;
+    private readonly ILogger<BceSmsClient> _log = log;
+    private readonly string _ak = cfg["BAIDU_SMS_AK"] ?? "";
+    private readonly string _sk = cfg["BAIDU_SMS_SK"] ?? "";
+    private readonly string _host = cfg["BAIDU_SMS_HOST"] ?? "smsv3.bj.baidubce.com";
+    private readonly string _signatureId = cfg["BAIDU_SMS_SIGNATURE_ID"] ?? "";
+    private readonly string _templateId = cfg["BAIDU_SMS_TEMPLATE_ID"] ?? "";
+
+    public async Task<bool> SendAsync(string phone, string code, CancellationToken ct)
+    {
+        var payload = new
+        {
+            mobile = $"+86{phone}",
+            template = _templateId,
+            signatureId = _signatureId,
+            contentVar = new { SMSvCode = code }
+        };
+        var body = Encoding.UTF8.GetBytes(JsonSerializer.Serialize(payload));
+
+        using var req = new HttpRequestMessage(HttpMethod.Post, Path)
+        {
+            Content = new ByteArrayContent(body)
+        };
+        req.Content.Headers.TryAddWithoutValidation("Content-Type", ContentType);
+
+        req.Headers.Host = _host;
+        var now = DateTime.UtcNow;
+        var timestamp = now.ToString("yyyy-MM-ddTHH:mm:ss'Z'", CultureInfo.InvariantCulture);
+        req.Headers.Add("x-bce-date", timestamp);
+        var auth = BceSigner.BuildAuthorization(_ak, _sk, "POST", Path, _host, now, body.Length, ContentType);
+        req.Headers.TryAddWithoutValidation("Authorization", auth);
+
+        using var resp = await _http.SendAsync(req, ct);
+        var respBody = await resp.Content.ReadAsStringAsync(ct);
+        if (!resp.IsSuccessStatusCode)
+        {
+            _log.LogError("百度短信发送失败 HTTP {Status}: {Body}", resp.StatusCode, respBody);
+            return false;
+        }
+
+        using var doc = JsonDocument.Parse(respBody);
+        var respCode = doc.RootElement.GetProperty("code").GetString();
+        if (respCode != "1000")
+        {
+            _log.LogError("百度短信发送失败 code={Code}: {Body}", respCode, respBody);
+            return false;
+        }
+        return true;
+    }
+}
diff --git a/backend/tests/Health.Tests/bce_signer_tests.cs b/backend/tests/Health.Tests/bce_signer_tests.cs
new file mode 100644
index 0000000..e9b37e1
--- /dev/null
+++ b/backend/tests/Health.Tests/bce_signer_tests.cs
@@ -0,0 +1,111 @@
+using Health.Infrastructure.Services;
+
+namespace Health.Tests;
+
+/// <summary>
+/// BCE v1 签名算法测试
+/// Golden value 由 Python 标准库 hmac + hashlib 按 baidubce-sdk 算法手算，
+/// 并与 baidubce-sdk 0.9.72 的实际 debug 输出对比验证一致
+/// </summary>
+public class BceSignerTests
+{
+    private const string Ak = "test-ak";
+    private const string Sk = "test-sk";
+    private const string Host = "smsv3.bj.baidubce.com";
+    private const string Method = "POST";
+    private const string ApiPath = "/api/v3/sendSms";
+    private const string ContentType = "application/json;charset=utf-8";
+    private const int ContentLength = 199;
+
+    private static readonly DateTime Ts1 = new(2026, 1, 1, 0, 0, 0, DateTimeKind.Utc);
+    private static readonly DateTime Ts2 = new(2026, 7, 23, 8, 0, 0, DateTimeKind.Utc);
+
+    // Golden 1: 固定输入
+    private const string ExpectedSig1 = "7592321b147186724a0194344aa274b4875fbc3442b4a5a07db4fd00cf44e580";
+    private const string ExpectedAuth1 = "bce-auth-v1/test-ak/2026-01-01T00:00:00Z/1800/content-length;content-type;host;x-bce-date/" + ExpectedSig1;
+
+    // Golden 2: 不同 timestamp
+    private const string ExpectedSig2 = "5c058909c04e8a6964fc22f9ae00cd5aae9c9182cb21fca7a76eb834eaa47c0b";
+
+    // Golden 3: 不同 SK
+    private const string ExpectedSig3 = "b944339bad2635d0eb41344427c1328f9785335a64baaabced658fa487fb228a";
+
+    // Golden 4: 不同 content_length
+    private const string ExpectedSig4 = "7b2f8bfdda2255b2331992a4adb9fb7365aa83c62453b61380cc7be350e6105f";
+
+    [Fact]
+    public void BuildAuthorization_FixedInput_MatchesGoldenValue()
+    {
+        var auth = BceSigner.BuildAuthorization(Ak, Sk, Method, ApiPath, Host, Ts1, ContentLength, ContentType);
+        Assert.Equal(ExpectedAuth1, auth);
+    }
+
+    [Fact]
+    public void BuildAuthorization_DifferentTimestamp_ProducesDifferentSignature()
+    {
+        var auth1 = BceSigner.BuildAuthorization(Ak, Sk, Method, ApiPath, Host, Ts1, ContentLength, ContentType);
+        var auth2 = BceSigner.BuildAuthorization(Ak, Sk, Method, ApiPath, Host, Ts2, ContentLength, ContentType);
+        Assert.NotEqual(auth1, auth2);
+        Assert.EndsWith(ExpectedSig2, auth2);
+    }
+
+    [Fact]
+    public void BuildAuthorization_DifferentSecretKey_ProducesDifferentSignature()
+    {
+        var auth1 = BceSigner.BuildAuthorization(Ak, Sk, Method, ApiPath, Host, Ts1, ContentLength, ContentType);
+        var auth3 = BceSigner.BuildAuthorization(Ak, "test-sk-2", Method, ApiPath, Host, Ts1, ContentLength, ContentType);
+        Assert.NotEqual(auth1, auth3);
+        Assert.EndsWith(ExpectedSig3, auth3);
+    }
+
+    [Fact]
+    public void BuildAuthorization_DifferentContentLength_ProducesDifferentSignature()
+    {
+        var auth1 = BceSigner.BuildAuthorization(Ak, Sk, Method, ApiPath, Host, Ts1, ContentLength, ContentType);
+        var auth4 = BceSigner.BuildAuthorization(Ak, Sk, Method, ApiPath, Host, Ts1, 100, ContentType);
+        Assert.NotEqual(auth1, auth4);
+        Assert.EndsWith(ExpectedSig4, auth4);
+    }
+
+    [Fact]
+    public void BuildAuthorization_Signature_Is64CharLowercaseHex()
+    {
+        var auth = BceSigner.BuildAuthorization(Ak, Sk, Method, ApiPath, Host, Ts1, ContentLength, ContentType);
+        var sig = auth.Split('/')[^1];
+        Assert.Equal(64, sig.Length);
+        Assert.Matches("^[0-9a-f]{64}$", sig);
+    }
+
+    [Fact]
+    public void BuildAuthorization_Format_HasCorrectStructure()
+    {
+        var auth = BceSigner.BuildAuthorization(Ak, Sk, Method, ApiPath, Host, Ts1, ContentLength, ContentType);
+        var parts = auth.Split('/');
+        Assert.Equal(6, parts.Length);
+        Assert.Equal("bce-auth-v1", parts[0]);
+        Assert.Equal(Ak, parts[1]);
+        Assert.Equal("2026-01-01T00:00:00Z", parts[2]);
+        Assert.Equal("1800", parts[3]);
+        Assert.Equal("content-length;content-type;host;x-bce-date", parts[4]);
+        Assert.Equal(ExpectedSig1, parts[5]);
+    }
+
+    [Fact]
+    public void BuildAuthorization_RealCredentials_MatchesSdkDebugOutput()
+    {
+        // 用百度 SDK 0.9.72 实际 debug 日志里的真实输入，验证 C# 输出和 SDK 完全一致
+        var auth = BceSigner.BuildAuthorization(
+            "ALTAKnJn8wtdLtBPgl7bD1x3N3",
+            "c5ca05a967d04a69bbc0e12f08062dc8",
+            "POST",
+            "/api/v3/sendSms",
+            "smsv3.bj.baidubce.com",
+            new DateTime(2026, 7, 23, 9, 3, 42, DateTimeKind.Utc),
+            199,
+            "application/json;charset=utf-8");
+
+        Assert.Equal(
+            "bce-auth-v1/ALTAKnJn8wtdLtBPgl7bD1x3N3/2026-07-23T09:03:42Z/1800/content-length;content-type;host;x-bce-date/0fd388266f63e9036de09981d7312ce3b7e279c8789823cb80b6c1800005fe13",
+            auth);
+    }
+}