The geometrical optics method(GOM) and Lorenz-Mie method were used to study the scattering properties of spherical particles at the wavelength of 0.55 μm, and the accuracy of the two methods were analyzed. The impacts of particle size parameter and the imaginary part of the refractive index on the forward scattering phase function of spherical particles were investigated. The results show that the scattering properties of spherical particles calculated by GOM and Mie are very close when the particle size parameter is greater than 60. When the particle size parameter is less than 1 000, the relationship of the forward scattering phase function with the particle size parameter can be described with a quadratic formula, and the results of GOM and Mie are identical with the increase of the particle size parameters, they gradually lose their quadratic relationships. When the particle size parameter is larger than 10 000, the GOM result is larger than that of Mie′s result. For a particle size parameter, the forward scattering phase function firstly increases and then decreases with the imaginary part of refractive index.