Abstract: Venus 1# sub-criticality assembly, which consists of both fast and thermal neutron spectra zones for accelerator driven sub-critical system (ADS) research in China, is a sub-critical system. The loaded assembly is driven by external neutron source with different neutron energy. The fission rate distributions on radial and axial aspect for fast and thermal neutron spectra zones’ fuel element were calculated by using MCNP code. The neutron energies of the external neutron sources were 2.5, 5, 14 MeV, respectively. The result shows that if the source strength is the same, the higher the neutron energy is, the larger the area of function is and the greater the fission rate is. On the other hand, if the neutron energy is the same, the fission rate distribution of the axis is lower on the both side and higher in the middle, while the radial fission rate distribution first decreases and then increases for fast neutron spectra zone and initially increases and then decreases and increases again when approching the reflector for the area of thermal neutron spectra zone. The calculating fission rate distributions provide a reference for follow up experimental measurements and detectors arrangement.