L -lactic acid is not only an important organic acid, but also one of raw materials of biodegradable materials poly(lactic acid). L -lactic acid was refined and extracted by esterification hydrdysis, the mature process conditions were that the proportion of lactic acid and methanol dosage was 1∶3.5, lactic acid concentration was approximately 85% ,the amount of sulfuric acid accounted for about 2.5% of total inventory, the esterification time was 2.5 h. Under the optimum process conditions, the total yield of ester hydrolysis process was from 70% to 85%, and the product quality was stable, the economic benefit was improved obviously.