Stress intensity factor at crack tip is the basis of studying the law of crack propagating, which indicates the critical degree of tending to crack at crack tip according to numerical style. The finite element method is used to analyze the crack stress intensity factors of overlay, the influence of parameters like overlay thickness, modulus, preliminary cracking length, temperature variation, and axes loading on crack intensity factors are studied, it offers theoretical basis for anti - cracking design methods of asphalt overlays.