Abstract: In order to optimize methods for determining the concentrations of anionic surface organic active substances in atmospheric fine particles, the Methylene Blue Spectrophotometric and Ethyl Violet Spectrophotometric Methods for the characterization of surface organic active substances in fine particles were optimized from two aspects-pretreatment and analytical parameters. In addition, the two optimized methods were applied to measure the mass concentrations of surface organic active substances in fine particle samples collected in Beijing. The results showed that:1) The optimal frequency, initial bath temperature and extraction time for ultrasonic extraction with the two methods were consistent:40 Hz, 30 ℃ and 35 min. 2) For the Methylene Blue Spectrophotometric Method, the optimal amount of chromogenic reagent was 0.35 mg of neutral methylene blue and 0.35 mg of acidic methylene blue, and the optimal standing time was controlled in the range of 30-45 min. 3) For the Ethyl Violet Spectrophotometric Method, the optimal amount of chromogenic reagent was 0.098 mg, the optimal standing time was 30 min, and the optimal amount of the auxiliary reagents were 0.4 mL of acetate buffer (pH=5), 10 μmol of EDTA and 0.25 mmoL of sodium sulfate. The determined values for the mass concentrations of the surface organic active substances in the fine particles were 0.14-0.39 μg/m³ and 0.14-0.47 μg/m³, respectively, acquired using the optimal experimental schemes for the Methylene Blue Spectrophotometric Method and the Ethyl Violet Spectrophotometric Method. Compared with the Methylene Blue Spectrophotometric Method, the Ethyl Violet Spectrophotometric Method has more convenient operation steps and a better linear standard curve. In conclusion, the Ethyl Violet Spectrophotometric Method is more applicable for the measurement of surface organic active substances in atmospheric fine particles.