Abstract: A test method is developed to simulate the deformation and strength characteristics of soils in real sites. This test method reveals the mechanism of seismic liquefaction of saturated sand under confined condition. A dynamic true triaxial test system is applied. This device provides mixed boundary conditions for samples and installation of advanced CATS test control system. The test results show that use of the dynamic true triaxial apparatus for sand liquefaction test research is feasible. Moreover, the mechanism of soil liquefaction under confined condition is investigated. Namely, the liquefaction will be generated when the axial and lateral pressures as well as the pore water pressure are equal to each other. It indicates that in the process of vibration load, the stress redistribution has a significant influence on the strength of sand liquefaction and the development mode of pore water pressure.