Bremsstrahlung will be produced when the metal target is bombarded by high energy electrons. Bremsstrahlung characteristics is discussed under the condition of optimal bremsstrahlung efficiency for the purpose of improving its quality. This paper simulates the bremsstrahlung characteristics, combining theoretical analysis with MCNP/4C program. Electron yield characteristics, photon yield of conic collimator, angular distributions and energy spectrum distributions are simulated for targets of different thickness and materials for 10 and 20?MeV electrons. The simulation results show that photon efficiency, emitted electron and photon flux distribution is related to material and thickness of the target. And the maximum photon yield of bremsstrahlung is mainly dependent on the electron energe range, and related to atomic number. Thus the relevant boundary conditions and characteristics are obtained under the optimal bremsstrahlung efficiency of different targets for 10 and 20?MeV electrons.