Abstract: In offshore soils there exists widely a kind if soil which mainly consists of silt and sand except clay with low plasticity. It is often considered a bearing layer of foundation. In this paper this kind of soil in the area of the south china sea where a gravity platform is to be constructed, is studied in the three cases: (1) behavior of static CU; (2) behavior under cyclic loading; (3) behavior of static CU after the soil has been cyclied. According to these laboratory results the mechanism is presented and discussed to explain its special mechanical behaviors