Abstract: A field water balance model has been developed in this paper. With the assumed boundary conditions,the long-term annual percolation of soil water (PSW) is simulated for one-meter depth soil horizon for cropping systmes of winter wheat/summer maize and winter wheat/bare soil. The results show that PSW is expressed as a linear function of seasonal precipitation,which is different in various cropping systems. PSW changes significanly in different hydrologic year types, which is 70~140mm more in humid years than in dry years. While in the winter wheat/bare soil it is 30~50mm more than in the winter wheat/summer maize.