[en] In order to fully understand the electron beam current amplification characteristic in diamond used in the diamond amplified photocathode as well as the relationship with other factors, a PIC module of VSIM was used to simulate the amplification characteristic of the electron beam current in diamond. The relationships among the secondary electron yield and the energy of the primary electrons, the internal field in diamond, the diamond film thickness and some other factors were obtained from the simulation results. The secondary electron yield could reach two orders of magnitude when appropriate primary electrons energy and internal field in diamond film were chosen. (authors)