The invention discloses a preparation method of porous graphene. The method comprises the steps of: (1) stripping graphite oxide in a water/ethanol mixed solution with pH of 9-10, adding a chemical foaming agent and mixing them uniformly, carrying out filtering and drying to obtain a solid mixture; (2) placing the mixture in a reducing atmosphere, and performing heating expansion reduction to obtain expanded graphene; (3) blending the expanded graphene with strong base, and conducting high temperature activation; and (4) washing the product with hydrochloric acid and deionized water, and performing drying so as to obtain porous grapheme. The porous graphene prepared by the method involved in the invention has a specific surface area up to 2075m<2>/g, a pore volume up to 1.8cm<3>/g, and an average pore size of 1-7nm. As a supercapacitor electrode material, the specific capacitance can reach 155F/g under a current density of 1Ag<-1>. As a porous graphene electrode, the specific capacitance can reach 84.4% along with the increase of current density from 0.2Ag<-1> to 20Ag<-1>. The porous graphene has high specific capacitance and cycle stability. The preparation method disclosed in the invention has the advantages of simple process, low cost, and easy scale production.