Finite element analysis model of the conduction-cooled package high power semiconductor lasers were established respectively to analyze normal stress, shear stress and displacement in reflowing process and operating process independently. With the help of analytical solution model, the cause and the distribution of thermal stress and smile were analyzed. The results show that shear stress is the origin of other thermo-mechanical behavior in reflowing process due to coefficient thermal expansion mismatch, while both coefficient thermal expansion mismatch and temperature gradient affect the thermal stress and displacement in operating process. In order to obtain the accurate result, the residual stress and displacement of reflowing process were considered as the initial condition in operating finite element analysis simulation, and the thermal stress and smile were simulated. The influence of heat sink temperature on smile was studied with finite element analysis and experiment. The result shows operating process has great impact on smile and results in worse smile, and with the rising of temperature of heat sink, smile also becomes larger.