The work aims to explore the mechanical principle of rail surface through corresponding theoretical research in view of the complex damage mechanisms of rail surface, so as to provide theoretical basis for practical applications. The problem was divided into two sub-problems based on the superposition principle. The wheel-rail contact force was obtained by function fitting. The first sub-problem was solved by Flamant’s solution of the concentrated force in the elastic mechanics and the second sub-problem was solved by the distributed dislocation technique. Further, two types of the singular integral equations about dislocation density were established. The numerical solution of the equations was presented by means of Gauss- Chebyshev quadrature method and the relevant mechanical parameters were obtained. The most dangerous position of the train running on the rail with edge crack, and the crack length of the open part and the stress intensity factor at crack tips (SIF) were obtained. The effects of different wheel weight, and the running state of the train (steady-state rolling or full sliding) on SIF were analyzed. The problem of the crack surface slip during the operation of the train was also analyzed. When the train is rolling steadily on the rail surface with long initial edge crack, the shear failure is the dominant, and the most dangerous position of the load is that the crack is located near the edge of the contact spot. When the train is running in the extreme state of full sliding, the magnitude and direction of stress on the crack surface will change, which will cause the crack surface state (opening or closed) to change as well. When the crack is shorter, the surface of rail is prone to open failure along the direction of depth.