Soil and water conservation measures(SWCM)of the Loess Plateau could control soil erosion by intensifying the infiltration and weakening the runoff.Therefore,the infiltration quantity is one of the important indexes that scale the effect of the soil and water conservation.The infiltration quantity was often calculated by the annual rainfall which products runoff.However,the little quantity rain or low intensity rain in the year has nothing to do with the conservation in the Loess Plateau.It could lead to the estimation error about the change of infiltration with SWCM.The infiltration variating with the catchment SWCM level incensement is studied based on the data of rainfall and runoff of the Xichuan catchment during 1997 to 2001.A gray dynamic model is put forward to the infiltration quantity tendency in the Xichuan catchment was predicted by a gray dynamic model,GM(1,1).The result indicates that the annual rainfall which can product runoff shows the effect of SWCM on infiltration more clearly than the total annual rainfall.The gray dynamic model can be used to predicat the tendency of infiltration.