Optical cavity ring down spectroscopy is a new type of spectroscopic d etection technique.It develops rapidly in recent years with the advantages of ultra-high sensitivity and l ow detection limit.In this paper, with the Beer′s law,the calculation methods of oscillation time and extinct ion coefficient are analyzed. Experimentally,an atmospheric aerosol extinction coefficient detection system is set up based on a 532nm pulse laser used as the light source and a high reflectivity confocal cavity use d as the cavity.The NO_2gases with different concentrations are used for calibration because of their different abso rptions coefficients.The detection limit of the system is 0.222μs,the stability is 0.18%,and the sensitivity is 1.47×10－7 m－1.Cavity mirror s with high reflectivity and pulse cavity ring down technology are quite feasible in the development of detecti on systems of aerosol extinction coefficients with high stability and sensitivity．