The invention discloses a method for preparing ethylene glycol and 1,2-propylene glycol by carrying out selective hydrogenolysis on high-carbon polyalcohol. According to the method, xylitol or sorbitol is used as a raw materials, water is used as a solvent, and a reaction is performed for 1 to 8h at a temperature of 140 to 220 DEG C, under H2 pressure of 2 to 10MPa and under a condition that an alkali additive and a catalyst exist; the catalyst uses CuM alloy as an active phase, and copper content is 10 to 85wt%; M is one or two of Fe, Co, Ni, W and Mo, and has content of 2 to 20wt%; a carrier is one of silicon dioxide, aluminium oxide, HZSM5 and SBA-15, and has content of 10 to 70wt%. According to the method disclosed by the invention,poison element Cr and heavy metal are not involved, and high hydrogenolysis activity, high target dihydric alcohol selectivity and recycling stability for the high-carbon polyalcohol are achieved under a mild condition.