Security and stability of the structure is priority in the dike engineering.The instability of dike would make economic loss or safety accidents.During the construction of the project of reclamation engineering in Zhoushan，slide of bagged-sand occurred when drainage sand quilt was laid.In this paper,the stability of sand quit is studied.By reviewing the geological survey data,and enumerating and eliminating all the stability factors,it is found that the surface mud is not explored and its physical and mechanical indexes are unknown,as well as the sparse sampling due to the inaccuracy of geological data.This paper gets the conclusion that the slide of bagged-sand is due to the composite factors,which are the lack of construction capability and incomplete geological survey.So this paper submits some construction scheme and summarizes experience and lessons from the case.