The invention provides a methanation method of heavy hydrocarbon, and belongs to the technical field of petroleum chemical engineering. Under the conditions of methanation of heavy hydrocarbon, heavy hydrocarbons and methane are simultaneously filled into a heavy hydrocarbon methanation reactor, then the mixture is contacted with a methane activation catalyst and a hydrogenation catalyst in sequence; under the effect of the methane activation catalyst, the methane is cut into CH3. and H., a hydrogen source is provided for the post hydrogenation reactions, and the directional assembly of CH3. and H. can be realized. The provided methanation method of heavy hydrocarbon can provide hydrogen for hydrogenation reactions, at the same time, can remove most of impurity atoms such as sulfur, oxygen, nitrogen, metals, and the like in heavy oil, and reduces the carbon residue. Moreover, the directional assembly of CH3. can convert heavy oil into light oil products, and increase the H / C ratio.