Carbon fiber paper (CFP) is currently the main product of the macroporous substrate (MPS) for the gas diffusion layer (GDL) of proton exchange membrane fuel cells (PEMFCs). The optimization of certain mechanical properties, electrical conductivity, thermal conductivity, air conduction, and mass transfer capabilities together with matched interaction can improve the core competitiveness of CFP. The artical conducts a detailed theoretical analysis of these conducting processes and principles based on CFP's main functions mentioned above. Thinner CFP with a wider pore channel brings about better mass permeability but unsatisfactory mechanical property. Thicker CFP with higher porosity and rougher surface results in worse electrical and thermal conductivity. Meanwhile, the temperature, pressure, time, and other fabrication parameters of CFP are also discussed. With so many contradictories, how to make a balance for real PEMFCs operation and reduce the cost would be a practical strategy for the optimization of CFP in the future.