diff --git a/internal/accounts/weighted.go b/internal/accounts/weighted.go
new file mode 100644
index 0000000..f744ace
--- /dev/null
+++ b/internal/accounts/weighted.go
@@ -0,0 +1,48 @@
+package accounts
+
+import (
+	"hash/fnv"
+
+	"github.com/wangjia/pay/config"
+)
+
+// Weighted 按 Weight 加权选账户,决策源为 hash(OutTradeNo)(确定性、可复现、跨节点一致,
+// 见计划 D1)。Weight<=0 记 1(对齐 model.Account gorm default:1)。retry 换号由
+// Router 的 ExcludeAccounts 过滤驱动,不依赖随机。
+type Weighted struct{}
+
+func NewWeighted() *Weighted { return &Weighted{} }
+
+func (Weighted) Pick(_ string, candidates []config.AccountConfig, hint PickHint) (config.AccountConfig, error) {
+	if len(candidates) == 0 {
+		return config.AccountConfig{}, ErrNoAccount
+	}
+	if hint.OutTradeNo == "" {
+		return candidates[0], nil
+	}
+	var total uint32
+	for _, c := range candidates {
+		total += weightOf(c)
+	}
+	if total == 0 { // 理论不达(weightOf>=1),兜底
+		return candidates[0], nil
+	}
+	h := fnv.New32a()
+	_, _ = h.Write([]byte(hint.OutTradeNo))
+	target := h.Sum32() % total
+	var acc uint32
+	for _, c := range candidates {
+		acc += weightOf(c)
+		if target < acc {
+			return c, nil
+		}
+	}
+	return candidates[len(candidates)-1], nil // 浮点无关的整数走位,兜底不达
+}
+
+func weightOf(c config.AccountConfig) uint32 {
+	if c.Weight <= 0 {
+		return 1
+	}
+	return uint32(c.Weight)
+}
diff --git a/internal/accounts/weighted_test.go b/internal/accounts/weighted_test.go
new file mode 100644
index 0000000..34a5067
--- /dev/null
+++ b/internal/accounts/weighted_test.go
@@ -0,0 +1,56 @@
+package accounts_test
+
+import (
+	"testing"
+
+	"github.com/wangjia/pay/config"
+	"github.com/wangjia/pay/internal/accounts"
+)
+
+func TestWeightedDeterministic(t *testing.T) {
+	w := accounts.NewWeighted()
+	cs := cands("a1", "a2", "a3")
+	// 同一 OutTradeNo 必落同一账户(确定性,可复现)。
+	first, _ := w.Pick("fake|global", cs, accounts.PickHint{OutTradeNo: "PAY-XYZ"})
+	for i := 0; i < 5; i++ {
+		got, _ := w.Pick("fake|global", cs, accounts.PickHint{OutTradeNo: "PAY-XYZ"})
+		if got.AccountID != first.AccountID {
+			t.Fatalf("同单号应恒定命中 %s, 第 %d 次得 %s", first.AccountID, i, got.AccountID)
+		}
+	}
+}
+
+func TestWeightedDistributesAndRespectsWeight(t *testing.T) {
+	w := accounts.NewWeighted()
+	// a1 权重 3,a2 权重 1 → 长跑大致 3:1。
+	cs := []config.AccountConfig{
+		{AccountID: "a1", Weight: 3},
+		{AccountID: "a2", Weight: 1},
+	}
+	counts := map[string]int{}
+	for i := 0; i < 4000; i++ {
+		no := "PAY-" + string(rune('A'+i%26)) + string(rune('0'+i/26%10)) + string(rune('a'+i/260%26)) + string(rune('0'+i%7))
+		got, _ := w.Pick("fake|global", cs, accounts.PickHint{OutTradeNo: no})
+		counts[got.AccountID]++
+	}
+	if counts["a1"] == 0 || counts["a2"] == 0 {
+		t.Fatalf("两账户都应被选中, got %+v", counts)
+	}
+	// a1 应显著多于 a2(3:1 容差:a1 至少是 a2 的 2 倍)。
+	if counts["a1"] < counts["a2"]*2 {
+		t.Fatalf("权重 3:1 未体现, got %+v", counts)
+	}
+}
+
+func TestWeightedZeroWeightTreatedAsOne(t *testing.T) {
+	w := accounts.NewWeighted()
+	cs := []config.AccountConfig{{AccountID: "a1", Weight: 0}, {AccountID: "a2", Weight: 0}}
+	counts := map[string]int{}
+	for i := 0; i < 400; i++ {
+		got, _ := w.Pick("fake|global", cs, accounts.PickHint{OutTradeNo: "N" + string(rune('0'+i%10)) + string(rune('a'+i%26))})
+		counts[got.AccountID]++
+	}
+	if counts["a1"] == 0 || counts["a2"] == 0 {
+		t.Fatalf("weight=0 应当 1 处理、两账户都可选, got %+v", counts)
+	}
+}