Abstract: Regarding liquefied sand as a fluid is a new method to study earthquake liquefaction.Based on the laboratory tests of the post liquefaction deformation,the flow characteristics of liquefied and post-liquefied sand,including the stress-strain rate and apparent viscosity,were analyzed from the viewpoint of fluid mechanics.The relative density,confining stress and liquefaction degree were the main factors in the tests.It was shown that the apparent viscosity of liquefied sand decreased with the increasing of strain rate,the liquefied sand was a kind of shear thinning non-Newtonian fluid under certain condition,and large strain might happen in the shear thinning state.With the reducing of pore pressure,the apparent viscosity of post-liquefied sand increased with increasing of strain and decreasing of pore pressure ratio.