Thermomechanical behavior has an important effect on reliability and lifetime of high-power diode lasers (HPDLs). Finite-element analysis (FEA) model and analytical solution model of the conduction-cooled package (CS) HPDL are established to analyze the thermomechanical behavior including normal stress, shearing stress, and displacement in reflowing process and working process. Moreover, in order to simulate and analyze the thermomechanical behavior in total process, reflowing thermal stress and displacement are considered as the residual stress and the initial condition of working process. We find that shearing stress is the origin of other thermomechanical behavior due to coefficient thermal expansion (CTE) mismatch, while both CTE mismatch and temperature gradient cause the thermal stress and displacement in working process. Although thermal stresses and displacement induced in reflowing process are larger than working process, the working process has great impact on smile and causes much worse total smile. The influence of different working temperatures on smile is also studied in total process with analytical solution, FEA, and experiment. For analytical solution, the total smile value is inversely proportional to the working temperature, while for FEA the smile value is proportional to the working temperature and FEA result accords with experimental result.