Abstract: MOCA program is used to design landmine detection device, and the process of landmine detection by prompt gamma neutron activation analysis (PGNAA) is simulated. The Northeast Normal University NG-9 neutron generator was used as the neutron source to study the influence of its internal insulating material (polyimide, etc.) on the neutron energy distribution. On this basis, the device was designed and optimized to determine the combination of tungsten, tungsten carbide and tungsten+boron-containing polyethylene+lead as the moderator, reflector and shield respectively. Compared with the distribution of singleenergy neutron sources, the thickness of the moderator, reflector and shield is reduced. The lutetium yttrium oxyortho silicate (LYSO) detector is used to detect gamma rays generated by landmines buried in soil with 5% water content at different depths. The hydrogen, carbon, nitrogen, and oxygen elements are analyzed to determine the effective depth of detection for anti-tank and infantry landmines, which shows that the designed device is feasible and can be used for actual PGNAA test research.