The invention discloses a low-temperature high-activity methanation catalyst and a preparation method thereof. The catalyst comprises metallic nickel as an active component, AL2O3 as a carrier and MgO as a structure auxiliary agent, and an appropriate amount of lanthanum oxide and manganese oxide are added as active auxiliary agents. The catalyst comprises the following main components in percentage by mass: 18-45% of NiO, 40-70% of Al2O3, 5-30% of MgO, 0.4-5% of La2O3 and 0.1-5% of MnO2. The catalyst disclosed by the invention has the advantages of large specific area, uniform nickel dispersity, good heat stability, strong oxidation resistance, low active temperature, adaptability to low hydrogen-carbon ratio and the like. The catalyst is applicable to preparation of LNG (liquefied natural gas) through methanation of industrial gases including coke oven gas, coal synthesis gas, semi coke exhaust gas and the like rich in CO, CO2 and H2, is particularly applicable to a methanation reaction in a low-temperature section, and can effectively improve the quality of synthetic natural gas. Meanwhile, the invention also provides the preparation method of the catalyst, and the preparation method is simple in process flow and can realize industrial production easily.