The invention discloses a polyimide-grafted sulfonated polyvinyl alcohol copolymer proton exchange membrane and a preparation method thereof. The proton exchange membrane is prepared by a casting filmof an organic solution of a polyimide-grafted sulfonated polyvinyl alcohol copolymer, so that the proton exchange membrane is available in raw materials, simple in process and low in equipment cost.According to the copolymer proton exchange membrane, the proton conductivity is effectively improved and the methanol permeability of the protein exchange membrane is reduced, thereby improving the comprehensive performance of the proton exchange membrane and solving the problem of methanol permeation when a Nafion membrane is applied to a direct methanol fuel cell; and the grafting ratio is changed and the sulfonation degree of polyvinyl alcohol is adjusted through adjusting the amount of carboxyl-containing diamine, so that the prepared polyimide-grafted sulfonated polyvinyl alcohol copolymer proton exchange membrane reaches the optimum balance between high proton conductivity and low methanol permeability. According to the proton exchange membrane disclosed by the invention, the protonconductivity can reach 111.4mS/cm, the methanol permeability is an order of magnitude lower than that of the Nafion membrane, and the proton exchange membrane can be applied to the direct methanol fuel cell and can also be applied to alcohol fuel cells, such as a direct ethanol fuel cell.