In order to study the impact of mixing ways of aerosols on their optical properties, one typical external mixing model plus three different internal mixing models of aerosols are introduced. The optical properties of mixed aerosol particles formed by black carbon, sulfate and organic carbon at 550 nm wavelength are calculated. The results show that there are great differences in optical properties of mixing particles and particle groups obtained by these models except Maxwell-Garnett model and Bruggeman model (difference less than 2%). Compared with externally mixed particle groups, the mass absorption factors of internally mixed particle groups are increased by about 20%, while the mass scattering factors of the particle groups are decreased by 10%~15% in most cases. The internal mixing models make a large enhancement of the mass extinction factors of mixed particle groups by 25% for maximum. Furthermore, the reduction of single scattering albedo is significant. In particular, the reduction of the scattering albedo of the mixed particle groups can be larger than 20% under circumstances that the volume ratio of black carbon is below 30% and the relative humidity is above 70%. In addition, optical properties of mixed particles, except the asymmetry parameter, are distinctly related to the change of volume ratio or relative humidity.