The mass concentration of aerosol particles is important for studying aerosol pollution. A method of retrieving mass concentration of aerosol particles is advanced with dual-scattering-angle optical particle counter, and the relationship is established among mass concentration, size distribution and density of aerosol particles. The method was validated by results measured at September 2004 and November 2007 in Beijing. It indicated that the method of retrieving mass concentrations of PM₁₀ and PM_2.5 is feasible, which supplied references to measure aerosol mass concentration using optical method.