The Brillouin scattering is the light scattering by the phonons in the solid. It is very useful for studying the structural phase transition in the crystal and measuring the elastic and photoelastic constants of the materials. To accomplish these goals, one has to be able to determine the linkage between the polarization of the scattered light and the phonon modes which can also provide insight into the origin of the phase transition. In our paper, we calculated the scattering factors using elastic equations, photoelastic relation and radiation equations for an orthorhombic crystal. The results are summerized in the Chart. From the Chart provided below one can easily find the correspondence of the phonon mode to the polarization of the scattered light.