Abstract: Proton exchange membrane water electrolyzer (PEMWE) is a promising clean renewable energy hydrogen production technology device, and it is also one of the key technologies of the space station's environmental control and life protection system. In microgravity, the bubble behavior inside PEMWE is extremely important for the energy conversion efficiency of the system. In this study, a multiphysics model based on electrochemical model coupled with fluid phase field was developed to compare and study the effects of basic parameters on bubble migration behavior and energy efficiency in PEMWE under normal gravity and microgravity environments. The results show that when the inlet water velocity increases from 0.1m/s to 0.5m/s in the microgravity environment, the bubble coverage rate of the lower wall increases by 9.5%, and when the runner depth is low, it is easy to form a thin film flow to block the lower wall of the runner. In the normal gravity environment, the inlet water flow velocity has little effect on the bubble coverage rate of the lower wall, but when the runner depth is low, it is still easy to form a thin film flow, which will block the runner. These studies provide valuable guidance for PEMWE's bubble management and energy efficiency improvement.