Abstract: The effect of laser surface strengthening is determined by the thermal circular principle.In order to obtain the reasonable quenching depth and distribution of the micro-hardness,the temperature field resulted from the laser strengthening must be analyzed exactly.The influence of the scanning parameters on the temperature field induced by the laser can be analyzed through the FEM.At the same time,the result form the simulation can be verified with the infrared measuring method.Finally,the conclusion can be drawn that the microstructure of the material surface can be improved effectively by the laser strengthening technology and the thermal circular principle can be affected by the change of the process parameters.