The invention relates to PVB (Polyvinyl Butyral) modified and phenolic resin reinforced carbon paper as well as a preparation process and application thereof, and belongs to the technical field of diffusion layers of fuel cells. A preparation method designed by the invention comprises the following steps of immersing carbon paper in a PVB solution for soakage, and taking the carbon paper out, so as to obtain the carbon paper provided with PVB through the soakage; afterwards, immersing the obtained carbon paper provided with the PVB through the soakage in a phenolic resin solution to carry out the soakage, taking the carbon paper out, and drying the carbon paper, so as to obtain the treated carbon paper; pressurizing the treated carbon paper to be 10MPa to 30MPa at 160 to 220 DEG C, and carrying out heat preservation, so as to obtain the completely cured carbon paper; and finally, the carbon paper is subjected to heat treatment, so as to obtain the PVB modified and phenolic resin reinforced carbon paper, wherein the temperature of the heat treatment is 1,800 to 2,500 DEG C. The preparation process provided by the invention is simple; and the prepared carbon paper has excellent performances of good flexibility, high strength and the like, and is convenient to industrially apply on a large scale.