Abstract: A new probabilistic model is proposed to evaluate the development of pore pressure in saturated sands under random seismic loading. The nonlinear dynamic property of sands, the uncertainty of liquefaction resistance and the nonlinearity of development of pore pressure are considered in the model. The cumulative distribution functions of pore pressure at the end of any cycle of loading are computed. The probabilities of liquefaction are directly obtained from the functions when the pore pressuie ratio is 1.0. Three typical sites of Niigata Earthquake are analyzed with the new method. The good agreement of the calculated results with field observation confirms the applicability of this method.