Abstract: In the late development stage of oilfield, the unfavorable factors of high water cut,high formation pressure drop,and high produced fluid and injection imbalance in pay section may cause formation depletion and operating fluid loss in sand-washing operation.Sand particles in well bore are hard to remove thoroughly.The mechanical sand-bailing technology makes sand-washing operation more efficient.It can remove sand pinnacle completely and raise workover benefit.The equipment and operational principles of the mechanical sand-bailing technology were introduced.Some operation notices were also suggested.Field test showed that this technology could avoid reservoir pollution and prolong the workover intervals.