SqlConnection con = DB.CreateConn();
con.Open();
try
{

string sqlstr0 = "delete from Teacher_course where Teacher_course.Teacher_id='" + Gv_teach.DataKeys[e.RowIndex].Value.ToString() + "'";
string sqlstr1 = "delete from Teacher where Teacher_id='"+Gv_teach.DataKeys[e.RowIndex].Value.ToString()+"'";
SqlCommand sqlcom0 = new SqlCommand(sqlstr0, con);
sqlcom0.ExecuteNonQuery();

SqlCommand sqlcom1 = new SqlCommand(sqlstr1, con);
sqlcom1.ExecuteNonQuery();
sqlcom1.ExecuteNonQuery();
Lbl_note.Text = "删除成功";
Lbl_note.Style["color"]="green";

}
catch (SqlException)
{
Lbl_note.Text = "删除失败";
Lbl_note.Style["color"] = "red";
}
con.Close();
St_BindGridView();

string sqlstr0 = "delete from Teacher_course where Teacher_course.Teacher_id='" + Gv_teach.DataKeys[e.RowIndex].Value.ToString() + "'";
string sqlstr1 = "delete from Teacher where Teacher_id='"+Gv_teach.DataKeys[e.RowIndex].Value.ToString()+"'";

你这两个Sql语句正确吗?
你自己检查一下啊

我改了还是不行啊

数据是能删除的,就不懂为什么不能在Lable控件中显示删除后的信息.

Lbl_note.Text = "";
你有这样的代码吗?
把它放在
if (!IsPostBack){
}
里

你断点一下看到第错在了哪里，自己仔细检查一下。