At present,infrared thermal imaging technology is widely concerned in China,and plays an important role in reconnaissance,surveillance,gun aiming,guidance,etc.As one of the important components in the thermal imager,the focusing component is the main mechanical structure to complete optical focusing.Whether the thermal imager can keep stable motion and meet the requirements in the focusing process directly affects the final imaging effect and tracking effect.In this paper,the force analysis and motor selection of cam focusing mechanism are carried out,and the factors of moment of inertia and friction moment are considered comprehensively.Through calculation and simulation analysis,the factors affecting cam efficiency are found,and optimization suggestions are put forward.