Abstract: Exposure buildup factors up to 40 mean free paths in ranging from 0.015 MeV to 15 MeV photon energy were calculated by using the Monte Carlo simulation code EGS4 for light concrete used in certain nuclear power plant. The calculation took into account effect of bremsstrahlung, fluorescence and coherent (Rayleigh) scattering on the buildup factor. Then, the corresponding fitting parameters of the G-P fitting formula were presented by the geometrical progression approximation fitting formula. The method can get the γ shielding buildup factors for any shielding thickness of the concrete and any photon energy.