Abstract: By means of digital image measuring technique of local deformation and the cyclic loading test machine,the triaxial cyclic loading test of sandy soil was devised,and the variation of axial,radial and volumetric deformations and Poisson’s ratio of sandy soils in different states were investigated.Expansion in loading and contraction in unloading were the behaviors of sandy soils.After many cycles of loading and unloading,the structural deformation of particles,such as slipping,rotating and crushing,would fade away in the end,and the structural deformation would arrive at a stabilization point.The variation of Poisson’s ratio was related closely with the change of volume of specimen.The range of variation for Poisson’s ratio could be analyzed from the change of volume.