In the system of temperature control of high-power semiconductor laser(LD),a high-precision pulse width modulation(PWM) power amplifier was designed based on the characteristics of temperature controller(thermoelectric coolers) by using single chip micro-computer.With the single chip micro-computer 89C51 as the central controller and 12 bit D/A converter,the system gained higher control accuracy.The conflict between dynamic range enlargement and controlling precision improvement was eliminated with the method of DAC norm voltages switching,and so,better cost-performance can be achieved.A new circuit D trigger-block delay circuit was also put forward to prevent MOSFET H-bridge arms from cross-connection.The output voltage error is 0.4%.