Preparation of lactitol

The invention discloses a preparation method of synthesizing lactitol with lactose as a starting material. In the method, lactose is taken as the starting material to synthesize the lactitol by one step. The preparation method comprises the following steps: taking potassium borohydride as a reducing agent and reacting at a suitable temperature to avoid a high-temperature and high-pressure reaction required before, and hydrolyzing with cation exchange resin and removing impurities with anion exchange resin during the reaction, thus obtaining the lactitol. On the basis of the prior art, the preparation method simplifies operation, overcomes the disadvantages of high-temperature and high-pressure strict reaction conditions required before, hard control on extent of reaction, and has the advantages of simple operation, high safety, good product quality, low cost and the like.