The invention discloses a preparation method of a wide-temperature range rare earth-based composite oxide denitration catalyst. The preparation method comprises that titanium dioxide and montmorillonite as carriers, ammonium metatungstate, ammonium metavanadate, cerium nitrate and manganese oxide as active components and accessory materials are subjected to blending, ageing decaying, kneading, molding, drying and roasting to form the wide-temperature range rare earth-based composite oxide denitration catalyst, wherein the accessory materials comprise monoethanolamine, citric acid, ammonia water, lactic acid, stearic acid, glass fibers, wood pulp, hydroxypropyl methyl cellulose, polyoxyethylene, citric acid and water. The preparation method utilizes the rare earth-based composite oxide as an active ingredient, shortens catalyst activation time, effectively controls a SO2/SO3 conversion rate, improves a catalyst temperature adaptation capability, widens a catalyst use temperature range from 320-400 DEG C to 150-420 DEG C, has denitration efficiency more than 90%, and can carry out ammonia spraying denitration operation at a denitration area temperature of 150 DEG C when a boiler is started.