The invention relates to a preparation method of glycol. According to the method, in the presence of a copper-based catalyst and under the condition of hydrogenation reaction, oxalic ester and hydrogen contact with each other. The copper-based catalyst is prepared by the following step: (1) adding a silicon source into deionized water, and adjusting pH value to 6.5-12 by the use of ammonia water to obtain a sol mixture; (2) mixing the sol mixture obtained in the step (1) and a copper ammonia complex solution and carrying out ammonia distillation to obtain a viscous and dense material; and (3) successively carrying out first drying, washing, second drying and roasting on the viscous and dense material obtained in the step (2). By the preparation method of glycol, conversion rate and selectivity are high, and impurity content of the product is low.