As the nuclear power plant paid more attention, radiation detector is getting more attention to ensure safety. In this study, proton exchange membrane electrolyzer is applied to the tritium detector. Conventional detection methods are difficult to completely separate gases, but using electrolysis can only extract hydrogen purely to minimize the effects of other species. This can improve the sensitivity and shorten the measurement time. In this study, the basic characteristics of the proton exchange membrane tritium electrolyzer were investigated to develop real time detector of underwater. Experiments were carried out in terms of the catalyst amount of the membrane electrode assemblies(MEA), the material of the separator plate, the supply flow rate, operating pressure and operating temperature, respectively. The current density is proportional to the amount of hydrogen generation and is advantageous when the voltage is low at the same current density. It was confirmed that the voltage was affected at the same current density depending on the cell operating conditions. And it was found that the shape of the flow path of the separator plate is required to be improved.