The numerical simulation program of neutron activation products and their radiation characteristics is an important tool to study the activation effect of materials. A numerical simulation program capable of simulating the neutron activation effect of materials was developed through the secondary development of the JMCT software, and it was named “neutron activation simulation program”, which is expected to be applied to the research of arms control verification and nuclear security. The correctness of the neutron activation simulation program in calculating the neutron transport and activation inside nuclear warheads was tested, and the calculation results are accurate. The activation effect of concrete floors under the irradiation of the fission neutrons from fissile materials was studied based on the neutron activation simulation program, and the calculation results furthermore prove the functions of the neutron activation simulation program.