Abstract: Proton exchange membrane fuel cell (PEMFC) is a completely clean energy conversion device that converts chemical energy into electrical energy through redox reaction of hydrogen and oxygen in the air at two electrodes, in which the gas diffusion layer (GDL), as a key component in the PEMFC, has a crucial impact on the cell performance. Carbon paper is widely used as a substrate material for GDL by virtue of its rich pore structure, excellent electrical conductivity and sufficient mechanical strength. In this paper, high-performance carbon paper was prepared by wet molding, by using a mixture of two lengths (10 mm and 3 mm) of short-cut carbon fibers and the effects of different ratios of the two lengths of carbon fibers on the performance of carbon paper were investigated. The results show that the carbon paper with the addition of 10 mm length carbon fiber at 30-50wt% has excellent overall performance, showing high porosity, air permeability, electrical conductivity and mechanical strength. The membrane electrode assembled by 10 mm length carbon paper with 30wt% carbon fiber content reaches a maximum power density of 1473 mW·cm⁻² at 60% RH, which is higher than the performance of the corresponding membrane electrode of commercial carbon paper (Toray). The electrochemical impedance spectroscopy (EIS) results indicate that the carbon paper prepared from the appropriate ratio of two lengths of carbon fibers has lower mass transfer impedance. It shows that the excellent dispersion of short carbon fibers and the high pore structure and mechanical properties built by long carbon fibers can achieve a balance between the properties of the carbon paper preparing process and meet the requirements as a gas diffusion layer material.