By the numerical modeling and experimental test, the influence of temperature on “smile” was studied. By using the finite element method, the thermal stresses induced during bar bonding and operating process were simulated respectively. In simulations, it is assumed that the deformation of the laser bar is only caused by the thermal stress. The simulated results show that the thermal stress across the laser bar decreases with the increasing of heatsink temperature. As thus, the curve of the laser bar induced by packaging thermal stress will decrease with the increasing of the temperature. In this experiment, “smile” of five samples from the same wafer and batch was measured under different heatsink temperatures. Experimental results show that “smile” of the five samples increases or decreases as heatsink temperature increasing. The possible reason which is related with the combined action between the primitive bending shape of the bare bar and the mounting thermal stress. If the bare bar before packaging is flat or convex, “smile” of the diode laser bar will decrease as the heatsink temperature increasing. In addition, if the bare bar is concave and the laser bar is still concave after packaging, “smile” will increase with the increasing of heatsink temperature.