The proton exchange membrane fuel cell (PEMFC) is an ideal energy conversion device. The performance of a fuel cell stack depends on the coordination of many aspects. Consistency is an important factor affecting the performance of fuel cell stacks. However, it is still not very clear how to evaluate and improve fuel cell stack consistency. In this review, the evaluation methods of fuel cell stack consistency are summarized, and various influencing factors of consistency are discussed, including operation conditions, operating mode, control strategy, structure design, component materials, and manufacturing processes. The membrane electrode assembly (MEA) is the core component of PEMFC, and the differences between MEAs also determine the voltage consistency of fuel cell stacks. The detection of MEA parameters is an important method to evaluate its quality, and the main detection methods of MEA parameters are reviewed and compared. Moreover, the influence of MEA parameters on the performance and lifetime of fuel cell stacks is systematically analyzed in this review. Finally, research orientations and methods for improving fuel cell stack consistency are proposed from MEA preparation, stack design, and operation optimization.