Abstract: Through the study on physical fitness and type, this paper discussed the influence of present farming system of corn belt on fertility degradation in Jilin Province. The results showed that the interface of the middle plough layer and plough sole under the present farming system was wavy type, while the interface of the plough layer and plough sole of the corn field under the cropping system of annual autumn plowing was flat type. Soil bulk density and composition of three phases of wavy plough sole were different significantly with those of plough sole. The organo-mineral complex and organic carbon content of the plough layer between two types had no significant difference, but had significant difference in bottom soil. The valid soil quantity of flat type was two times more than that of wavy type. Therefore, the water retention property and corn yield of flat soil profile were better than those of wavy soil profile. Little valid soil quantity is the main cause of fertility degradation of black soil in corn belt of Jilin Province.