One of the critical regulation issues for the development of a very high temperature reactor (VHTR) with a hydrogen production facility is the safety distance between a VHTR and a hydrogen production facility. The multi-energy method (MEM) was found as the effective correlation because it predicts an overpressure buildup rising from a detonation shock to a weak explosion. However, the MEM has several drawbacks that include the inability to predict an asymmetric explosion phenomenon. Therefore, we developed a CFD analysis methodology for predicting an overpressure buildup caused by a hydrogen explosion with an error range of approximately ±30% on the basis of test results. Furthermore, we observed the important physics of hydrogen explosion due to the small-scale obstacle through a comparison between the CFD results and the test results. The obstacle structure may delay the pressure wave propagation and give rise to a superposition of the pressure waves.