This paper visualizes explosions in a subsurface magazine model constructed underground to mitigate the effects of blast waves. Numerical simulations discuss the effect of water that is put inside the magazine model. In the case of the explosion inside the magazine with water, the peak overpressure on the ground becomes smaller than that in the case of the explosion on the ground. The peak overpressures on the ground agree with those in the previous experiment. The increases of kinetic and internal energies of water are then estimated, and that the internal energy transfer at the interface of water and air is one of important factors to mitigate the blast wave on the ground in the present numerical method. As high-pressure gas at the exit of the magazine model drives the blast wave, the exit impulse and pressure are calculated and well reduced in the case with water inside the magazine model. Our study confirms that the exit pressure can scale the peak overpressure on the ground. (C) 2016 Elsevier Ltd. All rights reserved.