In order to study the effect of potential function (L-J,Exp-6) on calculation of the reduced second Viral coefficient B^*(T^*), the Simpson′s changing step length integral was introduced to approximately calculate the different B^*(T^*). The calculation results are in agreement with literature values, which prove the availability of the calculation method introduced. By the comparison of B^*(T^*) L-J calculated by L-J potential function and B^*(T^*) Exp-6 calculated by Exp-6 potential function,the changing relationship between difference value(Δ(T^*)) and reduced temperature(T^*) was obtained. The result reveals that in detonation environment,when T^* is 25-40, there is obvious difference between B^*(T^*) L-J and B^*(T^*) Exp-6.