A computation model for the circumference surface cracks in the axis was founded based on the flexible fracture mechanics and complex function theory. According to the method based upon the surface cracks stress intensity factors, simulations were made by the influences of various crack length, load types, and axis’s diameters respectively. Stress intensity factors were able to achieve in various circumstance. Cracks stress intensity factors were given by different crack depths. And stress intensity factor of the axis under pulling force or torque was analyzed for the comparison.