The invention discloses a preparation method of 
carbon paper with a gradient pore structure, which comprises the following steps: separately degumming and oxidizing 
carbon fibers with different length-
diameter ratios, and respectively dispersing the treated 
carbon fibers in a dispersant solution to form carbon 
fiber slurry with different length-
diameter ratios; sequentially carrying out gradient layering and inclined net forming on the carbon 
fiber slurry according to the length-
diameter ratio of 
carbon fibers from high to low to obtain a 
carbon felt precursor with a three-dimensional net structure; dipping the 
carbon felt precursor in a resin solution, taking out the dipped precursor, and conducting 
drying to obtain a 
carbon felt; and firstly hot-pressing the carbon felt into 
carbon paper body paper, and then conducting 
carbonization and graphitization treatment to obtain the gradient pore structure 
carbon paper. According to the invention, gradient layering is carried out in sequence from high to low according to the length-
diameter ratio of the 
slurry carbon 
fiber, so that the prepared carbon paper has a gradient pore structure, communicating pores are formed in the carbon paper, the 
pore diameter changes in a gradient manner along the normal direction on the plane of the carbon paper, a pressure gradient is formed in a 
diffusion channel, the gas conveying efficiency can be improved, and the 
mass transfer and 
heat transfer performances of the carbon paper are effectively improved.