As a key component of the proton exchange membrane fuel cell hydrothermal management system, the membrane humidifier is strongly coupled with the operating parameters of the fuel cell. In this paper, a steady-state mathematical model of the membrane humidifier is established based on Matlab/Simulink, and the sensitivity simulation of the operating parameters and geometric parameters of the membrane humidifier is studied. The influences of inlet mass flow rate, temperature and pressure, membrane thickness and area on heat transfer, water transfer, relative humidity and water transfer rate of membrane humidifier on wet side and dry side were analyzed. The main conclusions are as follows: Improving the inlet mass flow rate can effectively improve the water transfer quantity, but reduce the water transfer rate. The higher temperature can enhance mass transfer, but the higher temperature will reduce the activity gradient, thus reducing the mass transfer on both sides of the membrane. Pressure mainly affects the moisture content of wet air. Under high pressure, the moisture transfer is lower, but the transfer rate is higher. A larger membrane area and a lower membrane thickness can improve the film moisture transfer and water transfer rate, which can effectively improve the membrane humidifier and fuel cell system hydrothermal management performance.