From the aspects of physics and chemistry, the processes and characteristics of soil degradation of typical rainfed farmland in the Horqin sandy land were discussed. Results showed that in the desertification process of rainfed farmland, a series of physical and chemical properties worsened associated with losses of soil fine particle materials, including bulk density and pH raised, total porosity reduced, aeration and non capillary porosity increased, water holding capacity relented, soil organic matter, total N and P, available N and P contents decreased. One percent of silt and clay contents (<0.05mm) were removed, could result in the decreases of 0.259 g/kg soil organic matter and 0.016 4 g/kg total N contents. Disturbances induced by farmers (i.e. cultivation of sandy grassland in the edge of farmland) was the main force of soil wind erosion and degradation. Two models of soil degradation process was put forward, namely, gradual degradation course and leap degradation course.