Abstract: The strength and deformation of Xinjiang expansive soils with different dry densities and different suctions were studied by use of the VJ unsaturated tri-axial apparatus.It was found that,the swell-shrinking of unsaturated expansive soils not only depended on the dry density and the confining pressures,but also closely related to the suction,and the dilation increased with the increase of the suction.In addition,the cohesion of unsaturated expansive soils increased nonlinearly and obviously with the increase of the suction and dry density.However,the variation of the suction and dry density almost did not influence on the effective angle of the internal friction.The ?b of Fredlund’s double variables theory was a continuously decreasing function in the interval of the suction instead of a constant.