1、引入Newtonsoft.Json的dll文件；引入Newtonsoft.Json命名空间：
DataTable转JSON字符串：
string josnstr = ""; string sql = "select ID,TestType from LbtTestTypes"; DataTable dt = SqlHelp.ExecuteDataset(SqlHelp.constr, sql, CommandType.Text, null).Tables[0]; if (dt.Rows.Count > 0) { josnstr = JsonConvert.SerializeObject(dt, new DataTableConverter()); } else { josnstr = "[]"; } return josnstr;List转JSON字符串：
public string LbtProjectInfo() { string josnstr = ""; List<RoadFlow.Data.Model.LbtTestTypes> list = btt.GetType(); if (list.Count > 0) { josnstr = JsonConvert.SerializeObject(list); } else { josnstr = "[]"; } return josnstr; } 相关博客： http://www.cnblogs.com/kissdodog/archive/2012/12/31/2841201.html