第一种方法：
        string ConnString = ConfigurationSettings.AppSettings["ConnectionString"];
         //创建一个SqlConnection
         SqlConnection Conn = new SqlConnection( ConnString );        

         string SQL_Select = "select id, ItemName from DDLItem order by id desc";

         //构造一个SqlDataAdapter

         SqlDataAdapter myAdapter = new SqlDataAdapter( SQL_Select, Conn);

         //開始读取数据

         Conn.Open();

         DataSet dataSet = new DataSet();

         myAdapter.Fill( dataSet,"Table1" );

         Conn.Close();

         //開始绑定DropDownList

         //指定DropDownList使用的数据源

         DropDownList1.DataSource = dataSet.Tables["Table1"].DefaultView;

         //指定DropDownList使用的表里的那些字段

         DropDownList1.DataTextField = "ItemName"; //dropdownlist的Text的字段

         DropDownList1.DataValueField = "id";//dropdownlist的Value的字段

         DropDownList1.DataBind();

另外一种方法：
        con.Open();
        SqlCommand cmd = new SqlCommand(strSql,con);
        SqlDataReader dr = cmd.ExecuteReader();
        while (dr.Read())
        {     
            DropDownList1.Items.Add(new ListItem(dr["status"].ToString(), dr["status_Id"].ToString()));
        }