Based on the hourly observational data of the aerosol scattering coefficient and the aerosol absorption coefficient as well as the coincidental data monitored by the GRIMM180 environment particle monitor in Chengdu during the period from September to December in 2017, the real and imaginary parts of the equivalent complex refractive index of “dry” aerosol at 550 nm were calculated using an immune evolutionary algorithm; subsequently, the correlations between these quantities and the primary index of mass concentration were further investigated. The results denote that the real and imaginary parts of the equivalent complex refractive index of “dry” aerosol are 1.55±0.045 and 0.022±0.0075, respectively. With respect to the change in the real part of the equivalent complex refractive index of “dry” aerosol, the most important mass concentration indexes of particles are the respective mass concentration ratios between particles having diameters smaller than 1 μm and particles having diameters smaller than 10 μm and 2.5 μm, and the corresponding determining coefficients are 0.53 and 0.21, respectively. With respect to the change in the imaginary part of the equivalent complex refractive index of “dry” aerosol, the most important mass concentration indexes of particles are the respective mass concentration ratios between black carbon and particles having diameters smaller than 10 μm and 2.5 μm, and the corresponding determining coefficients are 0.47 and 0.42, respectively.