int n = 0;
                string sqlsign = "select count(*) from HouseHold,DetailAccount where HouseHold.HouseID = DetailAccount.HouseID and HouseHold.Area = '" + comboBox1.Text.ToString().Trim() + "'";
                string sql = "select * from HouseHold,DetailAccount where HouseHold.HouseID = DetailAccount.HouseID and HouseHold.Area = '" + comboBox1.Text.ToString().Trim() + "'";
                OleDbConnection conn = dbObj.GetConnection();
                OleDbCommand comm = new OleDbCommand(sql, conn);
                OleDbCommand commsign = new OleDbCommand(sqlsign, conn);
                    conn.Open();
                    n = (int)commsign.ExecuteScalar();
                        comm.ExecuteNonQuery();
                        OleDbDataAdapter da = new OleDbDataAdapter(comm);
                        DataSet ds = new DataSet();
                        da.Fill(ds, "HouseHold");
                        for (int i = 0; i < n; i++)
                        {
                            dataGridView1.Rows[i].Cells["index_no"].Value = i+1;
                            dataGridView1.Rows[i].Cells["HouseID"].Value = ds.Tables["HouseHold"].Rows[i][0].ToString();
                            dataGridView1.Rows[i].Cells["theName"].Value = ds.Tables["HouseHold"].Rows[i][8].ToString();
                            dataGridView1.Rows[i].Cells["theOwner"].Value = ds.Tables["HouseHold"].Rows[i][2].ToString();
                            dataGridView1.Rows[i].Cells["Category"].Value = ds.Tables["HouseHold"].Rows[i][3].ToString();
                            dataGridView1.Rows[i].Cells["Area"].Value = ds.Tables["HouseHold"].Rows[i][5].ToString();
                            dataGridView1.Rows[i].Cells["Address"].Value = ds.Tables["HouseHold"].Rows[i][4].ToString();
   
                       }

messagebox.show( dataGridView1.Rows.Count.ToString());

------解决方案--------------------
先要添加行，才能对每个得进行操作
dataGridView1.Rows.Add()