Abstract: As the site of electrochemical reaction, the catalyst layer is an important component of proton exchange membrane fuel cells. In order to improve the performance and reduce the cost of proton exchange membrane fuel cells and considering the uneven distribution of reactants in the catalyst layer, the catalyst layer composition is designed to be the gradient distribution to improve the utilization of each component and reactant, thereby improving the cell performance without increasing the cost. The functional gradient catalyst layer is one of the important means to improve the cell performance. Therefore, the functional gradient distribution design of the catalyst layer is reviewed in detail from different components and directions in this paper. The gradient distributions of the catalyst layer components mainly focus on the catalyst loading and ionomer loading from three different directions of the fuel cell in different non-uniform distribution forms. The functional gradient catalyst layer can effectively improve the uniformity of reactant, temperature and current density distributions and improve the performance of fuel cells, which is one of the important means of the development of high-performance proton exchange membrane fuel cells.