Abstract: In this paper,a series of tests on Miyun sand-gravel specimens using a hollow cylinder torsional shear apparatus have been carried out to investigate the effect of α 0(the inital rotation angle of principal stress),p 0(average principal stress)and η 0 (stress ratio )on dynamic strength and pore pressure. The test results show that α 0 has important effects on the dynamic properties of soil. With the increase of α 0,dynamic strength decreases markedly.