Abstract: The modified Lade model and Barcelona unsaturated elastoplastic model are used to describe the stress and strain relationship of unsaturated clayey sand, The tests on three types of stress paths tests are conducted. The elastoplastic constitutive relations are deduced considering suction and net confining pressure at the same time. The changing laws of elastic strain, plastic strain, plastic work and yield function are given by adjusting the suction and net confining pressure. A formula for volume change that can express the stress dilatancy of unsaturated clayey sand is developed. The results of this formula agree with the test ones. It is shown that this theory is suitable for unsaturated clayey sand. At the same time, the peak value points and the stress dilatancy are greatly related to the net confining pressure and the matric suction.