Abstract: Light scattering measurement technology based on the classical Mie theory is widely used in the measurement of particle diameter and particle density measurement. The characteristics of light scattering from spherical particles in aerosol are analyzed with a numerical calculation method based on the classical Mie theory and discretedipole approximation (DDA) theory respectively. A numerical calculation method for intensity function and polarization ratio of the collimated incident beam scattered by small particles is given. The 3D graph for variation of the intensity function and polarization ratio with the relative physical parameters was obtained for the research of small particle scattering. The calculation results show that the results obtained by two methods based on DDA theory or classical Mie theory differ slightly when dimension parameter x＜4, and the results differ greatly along with the increase of dimension parameters. In comparison with the classical Mie theory, the DDA theory has greater potential in application since it may solve particle scattering problem for different shapes of particles.