[en] Fast neutron multiplicity measurement technology is an important attribute authentication technology. Under the premise of studying the basic theory, the Monte Carlo (MC) method is used to simulate the system structure and detection process by using Geant4 simulation toolbox and MCNPX, and then the fast neutron multiplicity distribution is solved by Matlab, The fast neutron multiplicity simulation platform with automatic modeling, neutron transport, data visual analysis and simulation, and cloud platform management data is designed and developed. Using the platform to carry out simulation calculation and experimental research on fast neutron multiplicity, the obtained fast neutron multiplicity distribution is consistent with the theoretical results. The simulation platform itself realizes quality mutual inspection, and the deviation between the simulation result and the experimental result is less than ± 10%. The research results show that the fast neutron multiplicity simulation platform has strong applicability and reliability and can be applied to the simulation measurement of nuclear materials. (authors)