Numerical simulation model of thermal loading on piston by laser is established. By virtue of the model,the influence of different cooling matters on thermal loading of piston is investigated. The results show that temperature fluctuations occur at thin-layer regional of piston top surface when cooling air is applied to piston top surface and tunnel with cessation laser heating,which is in accordance with actual stable conditions. Temperature fluctuations is not consistent with actual stable conditions of air cooling of piston inner chamber and tunnel or water cooling of tunnel. Low-cycle fatigue with air cooling of piston top surface,water cooling of inner chamber and tunnel can accelerate damage to piston. Meanwhile,these regions of concave,tunnel and inner chamber are most vulnerable to form crack due to the cool medium contacting with them. The numerical results are in agreement with the experimental results,which indicates that the established numerical mode is correct and reliable.