Abstract: In this paper the indexes of pore water pressure and dynamic strength of saturated sand are carried out under various stress conditions by applying double-action cyclic triaxial test system. These results can be used as a reference in the stabilily analysis of saturated sand foundations and slopes against earth-quake. Moreover, the V-phenomena in the wave peak of the time history of pore water pressure by the characteristic of volume swelling of dense sand under shearing stress are investigated.