By particle-in-cell (PIC) simulation and theoretically analysis, electron spatial distribution and energy distribution in the rod surface of rod-pinch diode(RPD) are obtained separately, as input parameters for Monte Carlo simulation of photon energy spectrum of X-ray emitted from RPD. The Monte Carlo simulation results show that the average photon energy of shot 09006 is 0.441 MeV. Taking account of Pb attenuator, the simulation results accord with experiment data detected by PIN detectors array.