Abstract: A material model which is suitable for both dry and saturated rocks under explosion loading, has been built. The plastic flow rule and the damage rate evolution equation were modified, for the purpose of numerical continuity and computational stability. Furthermore, the equation of state for saturated rock has been modified, thus the calculation agrees with experimental phenomena. Moreover, these modifications have been added into our SinoDyn dynamic code. With this code, the underground explosion effects in both dry and wet granites were numerically studied for many aspects. The calculated results agree well with the experimental data.