diff --git a/internal/model/dto/exchange_dto.go b/internal/model/dto/exchange_dto.go
index 24b19caa..49bbfb05 100644
--- a/internal/model/dto/exchange_dto.go
+++ b/internal/model/dto/exchange_dto.go
@@ -9,7 +9,7 @@ type CreateExchangeRequest struct {
 	FlowType       string  `json:"flow_type" validate:"omitempty,oneof=shipping direct" enum:"shipping,direct" description:"换货流程类型 (shipping:物流换货, direct:直接换货)"`
 	NewIdentifier  string  `json:"new_identifier" validate:"omitempty,min=1,max=100" minLength:"1" maxLength:"100" description:"新资产输入标识，direct 流程必填；卡支持 ICCID、接入号、虚拟号，设备支持虚拟号、IMEI、SN"`
 	MigrateData    *bool   `json:"migrate_data" description:"是否执行全量迁移，direct 流程未传按 false 处理"`
-	ExchangeReason string  `json:"exchange_reason" validate:"required,min=1,max=100" required:"true" minLength:"1" maxLength:"100" description:"换货原因"`
+	ExchangeReason string  `json:"exchange_reason" validate:"required,min=1,max=500" required:"true" minLength:"1" maxLength:"500" description:"换货原因"`
 	Remark         *string `json:"remark" validate:"omitempty,max=500" maxLength:"500" description:"备注"`
 }
 
diff --git a/internal/model/dto/exchange_dto_test.go b/internal/model/dto/exchange_dto_test.go
new file mode 100644
index 00000000..1dccb5fd
--- /dev/null
+++ b/internal/model/dto/exchange_dto_test.go
@@ -0,0 +1,34 @@
+package dto
+
+import (
+	"strings"
+	"testing"
+
+	"github.com/go-playground/validator/v10"
+)
+
+// 换货原因按字符计数，上限 500：从微信复制的多行说明（含换行）不超过 500 字都应通过校验。
+func TestCreateExchangeRequest_ExchangeReasonLength(t *testing.T) {
+	validate := validator.New()
+	multiLine := "862639070766110（门店：862639070766110机头，862639070743218后盖）\n\n" +
+		"862639070743218（厂家：862639070766110后盖，862639070743218机头）\n\n这两台后盖机头窜了。"
+	cases := []struct {
+		name    string
+		reason  string
+		wantErr bool
+	}{
+		{name: "多行说明124字", reason: multiLine, wantErr: false},
+		{name: "500个中文字", reason: strings.Repeat("换", 500), wantErr: false},
+		{name: "501个中文字", reason: strings.Repeat("换", 501), wantErr: true},
+		{name: "空", reason: "", wantErr: true},
+	}
+	for _, tc := range cases {
+		t.Run(tc.name, func(t *testing.T) {
+			req := CreateExchangeRequest{OldAssetType: "device", OldIdentifier: "862639070743218", ExchangeReason: tc.reason}
+			err := validate.Struct(req)
+			if (err != nil) != tc.wantErr {
+				t.Fatalf("wantErr=%v, err=%v", tc.wantErr, err)
+			}
+		})
+	}
+}
diff --git a/internal/model/exchange_order.go b/internal/model/exchange_order.go
index 322bab65..4c3d4932 100644
--- a/internal/model/exchange_order.go
+++ b/internal/model/exchange_order.go
@@ -56,7 +56,7 @@ type ExchangeOrder struct {
 	CompletedAt *time.Time `gorm:"column:completed_at;comment:换货完成时间，物流换货和直接换货完成后写入" json:"completed_at,omitempty"`
 
 	// 业务信息
-	ExchangeReason string  `gorm:"column:exchange_reason;type:varchar(100);not null;comment:换货原因" json:"exchange_reason"`
+	ExchangeReason string  `gorm:"column:exchange_reason;type:varchar(500);not null;comment:换货原因" json:"exchange_reason"`
 	Remark         *string `gorm:"column:remark;type:text;comment:备注" json:"remark,omitempty"`
 	Status         int     `gorm:"column:status;type:int;not null;default:1;index:idx_exchange_order_status;comment:换货状态 1-待填写信息 2-待发货 3-已发货待确认 4-已完成 5-已取消" json:"status"`