The finite element method and local stress and strain method were used to obtain the crack initiation life under fatigue load of each pit.  After getting the life of crack initiation,  the propagation life of initiation crack under pits bottom and the equivalent initial surface crack size were calculated through reverse integration of the Paris fatigue crack growth law and solving the non-linear equation using fracture model. Finally the nonlinear relation was set up between sizes of pits and equivalent initial surface crack by neural network.