Abstract: Based on main physical processes of secondary electron emission, the probability of secondary electron reaching the surface and emitting into vacuum at emission angles θ was deduced; the angular distribution of secondary electron released per primary electron entering polycrystalline obliquely was deduced, and the angular distribution of secondary electron released per backscattered electron was deduced. The angular distribution of secondary electron emitted from polycrystalline surfaces is formulated as cosinoidal function and independent of the incidence angle of the primary electron at high electron energy. It is concluded that the angular distribution of the secondary electron follow of the simple cosine distribution as the number of secondary electrons excited by primary electron and