MCNP program was used to simulate the radiation in the nuclear warhead model and calculate the effect of neutron and γ rays on the explosive decomposition. High energy secondary electrons activated by the rays made the molecular bond of the explosive broken and decomposed. To calculate concisely,four hypothese were given (1) the result from the action of rays causes the break of the explosive molecular bond; (2) the rays make the explosive decomposed in first order mainly; (3) the speed of explosive decomposition is uniform; (4) the total energy of which the rays left in the explosive makes the explosive decomposed. Through the four hypotheses and the amplifier of radiation intensity,a larger decomposition velocity was obtained. The results show that the decomposition velocity is not more than 10^－9 mol·a^－１,and the explosive decomposition caused by the radiation of nuclear warhead can be neglected,but the radiation affection can make the warhead warm and then affect the explosive decomposition.