BDU定义如下：

public struct ShucaiyiUnit
    {
        [DataMember]
        //数采仪编号
        public string MN { get; set; }
        [DataMember]
        //经度
        public string Longitude { get; set; }
        [DataMember]
        //纬度
        public string Latitude { get; set; }
        [DataMember]
        //SIM卡号
        public string SIM { get; set; }

}

原因：

忘记了下面的设置，呵呵

[ServiceContract(Namespace = "http://CY/EMP/EMPWebBLL/PMC/GIS") ]
    [ServiceKnownType(typeof(EmitionUnit))]
    [ServiceKnownType(typeof(PollutionSourceUnit))]
    [ServiceKnownType(typeof(ShucaiyiUnit))]
    public partial interface IGISWCF
    {
        /// <summary>
        /// 获取排口信息列表
        /// </summary>
        /// <returns>排口信息列表</returns>
        [OperationContract]
       List<EmitionUnit> GetGasEmitionUnitList(EmitionUnit unit);
        /// <summary>
        /// 获取排口信息列表
        /// </summary>
        /// <returns>排口信息列表</returns>
        [OperationContract]
        List<EmitionUnit> GetWaterEmitionUnitList(EmitionUnit unit);

/// <summary>
        /// 获取污染源信息列表
        /// </summary>
        /// <returns>污染源信息列表</returns>
        [OperationContract]
         List<PollutionSourceUnit> GetPollutionSourceUnitList(PollutionSourceUnit unit);
    }