This paper introduces the design of optics, constant current source and temperature controller of a high power semiconductor medical laser. The instrument adopts 980nm laser with maximum power output of 2W as therapeutic beam and 670nm laser of 3mW as aiming beam. The laser beams, after being collimated , can either be transmitted directly or be coupled through an optical fiber. Whole system is controlled by a microprocessor. With appropriate hardware and software , weVe achieved a variety of protection features which keep the laser diode from damage , and obtained an accurate and stable output, both of which are vital to a safe and reliable medical laser .