试试
Dim hc As New HttpClient("https://bsp-oisp.sf-express.com/bsp-oisp/sfexpressService")
hc.ContentType = "application/x-www-form-urlencoded"
Dim xml As String = "<Request service=""OrderService"" lang=""zh-CN""><Head>此处替换为您在丰桥平台获取的顾客编码</Head>......自己设置好报文内容 "
Dim checkword = "123" '此处替换为您在丰桥平台获取的校验码verifyCode
Dim encode As String = Convert.ToBase64String(New System.Security.Cryptography.MD5CryptoServiceProvider().ComputeHash(Encoding.Default.GetBytes(xml & checkword))) '加密报文
hc.FormData.Add("xml",xml )
hc.FormData.Add("verifyCode",encode )
Dim ret As String = hc.GetData()
msgbox(ret)