Abstract: The phenomenon of scattering cross section deviating from Rutherford scattering theory in Rutherford backscattering spectrometry was studied, and Rutherford scattering experiment was conducted by using computer simulation method. The simulation results demonstrate that the reason of small-angle divergence of Rutherford formula is that the condition of target atoms not covering mutually can not be satisfied, and the simulation results and Rutherford formula are same when the thickness of the target is so less that target atoms do not cover mutually and there is no numerous multiple scattering.