The false scattering and ray effect in spherical harmonics method, including P₁ and P₃ approximation, is studied. Physical models of parallel and oblique laser incidence into two-dimensional gray media are constructed and the temperature profile within the medium is investigated to examine the false scattering. The ray effect is analyzed by the net radiative flux in the boundary. Simulation results show that both false scattering and ray effect exist in the spherical harmonics method, and the ray effect is mitigated higher in P₃ than that in P₁ approximation. In addition, the ray effect in the spherical harmonics approximation mitigates with increasing optical thickness within gray medium.