The invention discloses a synthetic method of L-glucose. According to the synthetic method, sodium glucoseheptylate is used as a starting raw material, 2,2-dimethoxypropane is used for protecting hydroxyl completely; under an acidic condition, protecting groups are removed selectively; methyl ester is reduced into alcohol; the alcohol is oxidized into aldehyde; all the protecting groups are removed, and the target product L-glucose is obtained. The invention further provides a preparation method suitable for industrial production of L-glucose. According to the preparation method, L-glucose is prepared through the five steps of protection, selective protection, reduction, oxidation and deprotection, aftertreatment operation in each step is simple, only reduced compression, extraction, crystallization and other processes are involved, no chromatographic column separation operation is involved, the requirement for equipment is low, and the preparation method is suitable for large-scale production; the preparation method has a low requirement for equipment, industrial production can be achieved just through existing equipment, the yield in each step is high, is 70% or above and even reaches 100%, and cost is low; through the preparation method, the aftertreatment process of the product is simple, the product is easy to separate, and large-scale industrial production is easy.