Abstract: The excess pore water pressure in the saturated sand was controlled by applying the back pressure to the stratum,so that the degraded saturated stratum with the residual pore water pressure was simulated.Model tests of the soil-pile interaction were conducted to study variations of p-y curves and ultimate lateral resistances of single pile in degraded saturated sand with the increase of the residual pore water pressure.The following results were obtained based on model tests corresponding to the saturated sand with the relative density of 30%.The lateral resistance of the pile gradually decreased with increase of the residual pore water pressure under the same lateral displacements of piles.If there was no residual pore water pressure in the saturated sand,the ultimate lateral resistance of the stratum determined based on model tests was close to the academic value.The ultimate lateral resistances of piles degraded about 30%,55% and 80% respectively if the residual pore water pressure was 0.25,0.5 and 0.75 times the effective overburden pressure of the stratum.The ultimate lateral resistances of the stratum degraded about 90% for liquefied sand,which was consistent with shaking table and centrifugal model test results.