The invention discloses a preparation method of a porous ruthenium dioxide and manganese dioxide combined electrode. The preparation method of the porous ruthenium dioxide and manganese dioxide combined electrode comprises the following steps of mixing potassium permanganate, thick sulfuric acid and deionized water, obtaining mixed solution after evenly stirring, immersing substrate and obtaining a substrate-loaded precursor comprising manganic after hydrothermal reaction of 60 to 110 DEG C water; roasting the substrate-loaded precursor comprising manganic under 200 to 500 DEG C under argon atmosphere and obtaining manganese dioxide which is loaded on the substrate after cooling; mixing ruthenium chloride and water to obtain ruthenium salt solution, immersing the manganese dioxide which is loaded on the substrate to the ruthenium salt solution and performing aftertreatment to obtain the porous ruthenium dioxide and manganese dioxide combined electrode. According to the porous ruthenium dioxide and manganese dioxide combined electrode, the porous manganese dioxide directly grows on the substrate, nano ruthenium dioxide particles are loaded on the porous manganese dioxide, and a porous structure is maintained after loading of the ruthenium dioxide.