foreach (DataListItem di in DataList1.Items)
        {
            CheckBox cb = new CheckBox();
            DataList ds = (DataList)di.FindControl("DataList2");

            //for (int i = 0; i < ds.Items.Count;i++ )
            foreach (DataListItem dli in ds.Items)
            {
                 cb = ((CheckBox)ds.FindControl("CheckBox1"));

                if (cb.Checked)
                {
                    //string id = ds.DataKeys[] ； 取选中的主键
                  }
                
                ......
             }
         }