Abstract: A method for measuring atmospheric aerosol extinction coefficient was introduced. The coefficient was obtained by detecting the attenuation of light intensity when semiconductor laser passed through the aerosol. The light intensity values were detected, and after photoelectric conversion, signal processing and AD sampling, the aerosol extinction coefficient was calculated according to Lambert-Beer theorem. The dual-channel measurement method was used in the design, in order to reduce the effect of atmospheric molecules and the instability of the semiconductor laser light. The aerosols of different concentrations were tested. The results showed that the relative error was less than 4%. The atmospheric aerosol measurement system has the advantages of small size, simple operation and fast detection. It could be used to monitor air pollution and visibility.