Abstract: Proton exchange membrane (PEM) water electrolysis for hydrogen production has become a core technology for large-scale green hydrogen generation due to its fast response, high hydrogen purity and good adaptability to fluctuating renewable energy power generation. Improving the system efficiency and service life of electrolyzers, as well as ensuring efficient and stable system operation, are crucial for the development of PEM water electrolysis technology. To address the complex multiphysics coupling, uneven fluid distribution and non-uniform temperature distribution inside the PEM electrolyzer stack, a three-dimensional, two-phase, non-isothermal steady-state stack model consisting of four single cells was established based on COMSOL Multiphysics. The effects of water feeding mode, inlet water temperature and inlet water flow rate on the polarization characteristics, temperature field distribution and hydrogen production performance of the stack were systematically investigated. The results show that the uneven fluid distribution in the manifold leads to significant differences in flow velocity, temperature and voltage among the cells along the water inlet direction, with a maximum voltage difference of up to 0.03 V between cells at high current density. The cathode water feeding mode can enhance heat dissipation, promote hydrogen discharge and maintain membrane humidification, effectively avoiding local overheating. In contrast, without cathode water feeding, heat accumulates inside the stack, and the maximum temperature exceeds 360 K. Increasing the inlet water temperature can reduce the stack voltage, and it is recommended to control the temperature within 343-353 K (70-80 ℃) to prevent membrane aging. Increasing the inlet water flow rate helps reduce the mass transfer overpotential and alleviate local overheating, but an excessively high flow rate will increase pumping power consumption. The research results provide a theoretical basis for the optimization of operating parameters and structural design of PEM electrolyzer stacks.