The proton exchange membrane water electrolyzer (PEMWE) has the advantages of simplicity, small size, high current density, and high operating temperature, but it is easy to cause corrosion and oxidation to the gas diffusion layer or electrode at the oxygen end during electrolysis, which will accelerate the degradation of its performance. Therefore, a flexible 3-in-1 microsensor (temperature, voltage, and current) was developed using MEMS technology and embedded inside the PEMWE used in this study, and the circuit was designed and the data was observed in real time by Arduino Mega 2560. When the PEMWE is running, it can predict the performance in advance and obtain valuable information about the aging or failure of the PEMWE, so that it can be warned and adjusted in time.