Taking Monte-Carlo method to simulate the aerosol aggregate particles and discussing the porosity characteristics of aggregate particles, the effects of spatial shape and number of original particles on the porosity and effective refractive index of aggregate particles are analyzed. According to the electrical structures of substance, the aerosol aggregates particle are dispersed into a series of dipoles, and by discrete dipole approximation method, the statistical average values of scattering, absorption and extinction cross sections of aerosol aggregate particles with different porosities are obtained. The results show that the porosity of aerosol aggregate particles significantly depends on the spatial shape and number of original particles of aerosol aggregate particles. The effective refractive index, absorption, scattering and extinction cross section decrease with the porosity increasing. The findings can provide a reference for a comprehensive understanding of the optical properties of aerosol particles, and for the optical property of some coating materials by changing the porosity of aggregate particles in the coating material. This affects the effective refractive index of the coating material so that the light scattering and absorption of the coating material are changed.