Numerical simulation has been carried out to analyze temperature variation for laser diode welding system. The laser diode is assembled with cap and stem by projection welding, and temperature distribution is largely affected by the applied voltage, current, and welding duration. Maximum temperature happens a little later with heating peak and these material characteristics such as melting point are to be considered with temperature variation during the welding procedure. The results from this study could be applicable for optimal design of laser diode welding system.