The scheme relates to a method for preparing reduced isomaltooligosaccharide, which belongs to the technical field of preparation of starch sugar derivatives. In the method, isomaltose hypgather is taken as a raw material, and hydrogen is added under high temperature and a high pressure so as to perform a hydrogenation reaction, so that the reduced isomaltooligosaccharide is obtained. The production method of the reduced isomaltooligosaccharide comprises the keys as follows: isomaltose hypgather is added with hydrogen under high temperature and high pressure, the temperature is controlled between 80 to 140 DEG C, and the pressure is controlled between 6 to 10Mpa. The reduced isomaltooligosaccharide that is prepared by adopting the method achieves favorable heat resistance and stability to acid and alkali; a maillard reaction is avoided; and meanwhile, exceptional physiological performance characteristics of isomaltose hypgather can be kept.