arraylist的add问题，在线等！

为什么我第一次cellInfo.add放了一个对象后，第二次添加，会将cellInfo里的两个数据都变成第二次添加的对象，第三次会变成3个第三次添加的对象。郁闷。怎么改正啊？
public void replace(DataGridViewRow datarow, string str, string[] strs, int num, int drc)
        {
                if (num == 8)
                {
                    if (datarow.Cells[str].Value.ToString() != strs[num])
                    {
                        datarow.Cells[str].Value = strs[num];                        clsChangedCellsInfo.RowID = drc;
                        clsChangedCellsInfo.ColumnName = str;
                        clsChangedCellsInfo.ChangeTime = DateTime.Now;                        cellInfo.Add(clsChangedCellsInfo);//!!要怎么改这附近？
                    }
                }
                else
                {
                    if (datarow.Cells[str].Value.ToString() != strs[num])
                    {
                        double dStrs;
                        if (strs[num] == "")
                        {
                            dStrs = 0;
                        }
                        else
                        {
                            dStrs = Double.Parse(strs[num]);
                        }
                        
                        double dDatarow;
                        if (datarow.Cells[str].Value.ToString() == "")
                        {
                            dDatarow = 0;
                        }
                        else
                        {
                            dDatarow = Double.Parse(datarow.Cells[str].Value.ToString());
                        }
                        
                        if (dStrs > dDatarow)
                        {
                            dgvData.Rows[drc].Cells[str].Style.BackColor = Color.Red;
                        }
                        else
                        {
                            dgvData.Rows[drc].Cells[str].Style.BackColor = Color.Green;
                        }
                        datarow.Cells[str].Value = strs[num];                        clsChangedCellsInfo.RowID = drc;
                        clsChangedCellsInfo.ColumnName = str;
                        clsChangedCellsInfo.ChangeTime = DateTime.Now;                        cellInfo.Add(clsChangedCellsInfo);//!!)要怎么改这附近？
                    }
                }
            }
        }