This paper introduced the design principle and realization method of a kind of high precision optical power meter based on STM32, and gave its data processing and correction method. The optical power meter used STM32 as microcontroller, with the use of an InGaAsPIN photodetector to realize photoelectric conversion, and by the use of a lownoise photoelectric amplifier AD795 and highspeed multichannel analog switch to build circuit to achieve automatic range switching control in the measurement range of optical power, it can not only eliminated the nonlinear error of measurement, but also can improved the measurement dynamic range and accuracy. At the same time, use a 24bit ADS1232 ADC to achieve high measurement resolution, and with the help of data processing and modified technology to further improve the measurement accuracy, decrease the measuring error. The actual test results showed: the optical power meter has the advantages of low cost, high precision and reliable performance, can meet the demand of optical power test in engineering application.