Abstract: The dismantlement authentication of nuclear warhead is an important study in the field of nuclear disarmament and arms control verification. After the dismantlement of the nuclear warhead, the dismantled special nuclear material (SNM) and high explosive (HE) should be detected and authenticated by the verification team to ensure the SNM and HE from the nuclear warhead. In this paper, the authentication method of the explosive dismantled from WgU warhead (nuclear warhead with weapons-grade uranium core) was studied, and an authentication method based on the neutron irradiation was proposed. A numerical simulation platform based on the Geant4 software was established and used to study the feasibility and effect of the method. The results show that the verification team should set the irradiation time unilaterally, and set proper dismantlement time of the WgU warhead. By detecting the β⁺ decay of ¹³N and ¹¹C of the dismantled explosive, the explosive dismantled from the real WgU warhead and the fake explosive can be discriminated, which furthermore provides the important evidence for judging whether the explosive is mantled from the WgU warhead.