Abstract: For 24Na activity measurement of human body activated by neutron irradiation in the supercritical accident, the MCNP code is used to create a Monte Carlo simulation model. Two--ray total-energy peak detection efficiency of 24Na decay using different types of NaI detectors, and total -ray number detection efficiency of 24Na decay using plastic scintillator detector are simulated. The simulation results show that, for the 1.38 MeV and 2.76 MeV rays of 24Na decay, the efficiency of the well-type NaI detector is 4.30 times and 4.11 times that of the cylindrical one; the -ray detection efficiency of 24Na decay using the plastic scintillator detector is 1.72 times the 24Na ray detection efficiencyusing the NaI detector. Meanwhile, a rough calculation of the relationship between the detector counts and the neutron irradiation dose of human body is carried out.