试试这个:

private void btn_Delete_Click(object sender, EventArgs e) 
{       
    if (rdb_Delete.Checked)
    {
        foreach (DataGridViewRow row in DataGridView1.SelectedRows)
        {
            //delete record and then remove from grid. 
            // you can use your own query but not necessary to use rowid
            int selectedIndex = row.Index;         

            // gets the RowID from the first column in the grid
            int rowID = int.Parse(DataGridView1[0, selectedIndex].Value.ToString());
            string sql = "DELETE FROM Table1 WHERE RowID = @RowID";

            // your code for deleting it from the database
            // then your code for refreshing the DataGridView

            DataGridView1.Rows.Remove(row);
        }
    }
}