By means of the Mie scattering theory, the absorption efficiency factor and other optical factors of hygroscopic aerosol made of NaCl and H2O as well as (NH4)2SO4 and H2O which are set as the typical example are calculated, and the equivalent absorption coefficients with time of them are analyzed. The influence on the equivalent absorption coefficient when ignoring the energy absorbed by particles themselves is analyzed and the relative error of the equivalent absorption coefficient considering and ignoring the energy absorbed by the particles themselves is 234.7% and 255.2% at the time 1 μs, and the influence of different relative humidities and wavelengths on it is discussed. The relative errors of the results calculated by an uniformly mixed model are discussed, and the relative errors of the real results and calculated results are maximum at the time 1 μs which are less than 3.62% and 7.07%, respectively.