Proton exchange membrane fuel cells （PEMFCs） can achieve higher power by expanding the reaction area of the stack active area. However， for stacks with enlarged reaction areas， there is a tendency for increased non-uniformity in the distribution of membrane electrode assembly （MEA） stress， leading to a decline in the electrochemical performance of fuel cells. In this study， four different structural sizes of PEMFC stacks were designed. Using a combination of the equivalent stiffness model and finite element software， the impact of stack structures with expanded reaction areas on the uniformity of stress distribution of the MEA was analyzed. Furthermore， the installation position of steel belts within the stack was optimized to enhance the uniformity of internal contact pressure distribution. The research results indicate that the uniformity of MEA contact pressure distribution is particularly sensitive to changes in the reaction area width. When the size of the active area is widened， the standard deviation of the average stress within the stack’s internal active region increases by 23.2%. Conversely， when the active area is lengthened， or both lengthened and widened simultaneously， adding a corresponding bundled steel belt reduces the standard deviation of the average stress within the stack’s internal active area by 8.6% and 8.7%， respectively. This suggests that appropriately increasing the number of bundled steel belts can improve the uniformity of contact pressure distribution within the stack. Additionally， optimization results for belt positioning show that the more the outer steel belt is positioned closer to the end plate side， the more uniform the stress distribution within the stack’s internal active region.