A crankcase explosion relief valve (CERV) is installed to minimize the effects of explosions occurring in the crankcase of marine engines. According to the regulations of the International Association of Classification Societies (IACS), installation of CERV is mandatory and it must be designed and manufactured based on the engine size. As there are various types of engines, the CERV must be developed accordingly. A high cost is required for the explosion test in the development process, so the test is performed for verification purposes in the final development stage. However, if the developed CERV causes an inappropriate result that is different from the expected performance in the explosion test, it needs to return to the development process so conducting the explosion test in the final stage may be unreasonable. In this study, to predict CERV performance, the chamber and CERV were modeled in 2D, and numerical analysis was performed assuming that the DISC of the CERV was opened by causing an explosion inside the chamber. The results of the numerical analysis were verified by comparing the results with the pressure rising during the explosion. In addition, the reasonable results were obtained for temperature, pressure, and combustion products through comparison to the theoretical calculation results. If the numerical analysis method used in this study is applied, it is expected to be able to predict the performance and reactants at the stage before the explosion test when developing the crankcase explosion relief valve.