Abstract: in this article the oil crust is simulated by the paraffin, and the 1.25MeV γ ray of 60Co is irradiating by acute angle. We have accepted the scattered γ ray photons both in the acute and large scattering angles, and we give out a linear relation exists between the counting numbers of the scattering γ rays and the thickness of the paraffin. The experimental result implies that the result of the small angle scattering method better than the result of the large scattering angle method.