The invention discloses a low-density polyethylene / corncob composite foamed sheet and a preparation method therefor. The composite foamed sheet is prepared from the following raw materials in parts by weight: 88-102 parts of low-density polyethylene, 47-69 parts of full-starch plastics, 23-34 parts of corncobs, 28-42 parts of Miscanthus floridulus, 7-13 parts of chlorinated petrolatum, 24-37 parts of ramie stems, 5-10 parts of peat wax, 4-7 parts of glyceryl triacetyl ricinoleate, 2-4 parts of antimony penta(isooctyl thioglycolate), 15-25 parts of chestnut shells, 10-15 parts of glass fibers, 4-6 parts of aluminum phosphite, 15-20 parts of graphite crucible wastes, 5-10 parts of allophane, 10-15 parts of neopentyl glycol dibenzoate, 14-22 parts of white onyx and 20-30 parts of rice hulls. The foamed sheet prepared by the method is excellent in comprehensive performance, has relatively high mechanical strength and also has excellent heat resistance, corrosion resistance, impact resistance, wear resistance and heat preserving and insulating properties.