Computational fluid dynamics is a useful tool for investigating various cases when estimating the physical hazard of high explosives. This paper presents a test case to discuss the effect of a rigid barrier wall on the blast wave behavior of a high explosive. A condensed matter analysis program for high-energy materials (KHT2009) was used to obtain the properties of the detonation products. We modeled the detonation products with the equation of state for an ideal gas, and the initiation process of the high explosive was neglected. The wall was close to the high explosive and interacted with the initial blast wave and detonation products. An additional higher wall was installed over a standard barrier wall around an azimuth angle of 0°. The azimuthal distributions of the peak overpressures were compared for previously obtained experimental results and the present numerical results. The multiple reflected and diffracted waves off the wall produced complex flow patterns that were responsible for the azimuthal distribution of the peak overpressure. To secure a longer distance and time before the reflected wave from the additional higher wall intensifies the incident blast wave along 180°, and to achieve greater mitigation beyond and near the wall along 0°, we recommend that the additional higher wall be located as far as possible from the high explosive.