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.