Abstract: It is unavoidable that the hardness in the laser scanning area is not uniform due to the laser overlapping.Furthermore,the crack is apt to appear in the overlapping area.Firstly,the varying principles of the thermal cycle and stress during the laser scanning can be explained through the numerical methods.As a result,the theoretical explanations of the formation of the tempering and second quenching area are shown.The simulation results indicate that different overlapping parameters have little influence on the temperature varying principles.On the other hand,the parameters should not set too large in order to reduce the ununiformity of the hardness and crack in the area.