Abstract: PNFN was a method for uranium exploration. Pulsed neutron source was used, prompt fission epithermal neutron or delayed fission thermal neutrons were detected by using 3He neutron detector. Under the condition of different uranium content and porosity, the PNFN responses were simulated by using the MCNP code. The relationship between fission neutron and formation condition was studied. The obtained results showed that the larger the formation porosity, the lower the calculated uranium content. The precision of uranium content could be increased by the correction of scattering cross-section obtained by prompt fission epithermal or thermal neutron time decay spectrum method.