The invention discloses a lubricating oil composite filter aid and a preparation method thereof. The composite filter aid is prepared through the steps of preparing materials, acidizing, washing, drying, roasting, sieving and mixing. The composite filter aid is prepared from materials of inorganic mineral substances and organic cellulose, wherein the mass percent of the mineral substances is 50 to 90%, and the mineral substances are chosen from at least two of activated clay, kieselguhr, bentonite, activated carbon, perlite, zeolite, attapulgite, sepiolite, vermiculite, activated aluminum oxide, coal ash, steel slag micropowder and superfine slag powder; the proportion of the organic cellulose is 10 to 50%, and the organic cellulose is chosen from one or more of saw powder, wood bit, bagasse, bran, paper pulp, rice hull, bamboo residue, straw shred residue and lignocellulose. The lubricating oil composite filter aid has the advantages of convenience in use, quick filtering speed and good cleaned oil quality, capability of serving as a filtering agent in a lubricating oil clay refining period and suitablity for adsorbing and filtering technologies of other petroleum products, and the cost is low.