The invention relates to the technical field of food processing, in particular to a high-fiber-content sugar-free steamed cake and a preparation method thereof. The problem is solved that the sugar content of a cake is high, and on the basis of not adding sugar, the steamed cake has the same flavor and appearance as a sugar processed cake; raw materials include fruits, wheat bran, cellulase, pectinase, flour, eggs and edible oil; the wheat bran is grinded and then puffed, after the fruits are pulped and then mixed with the puffed wheat bran, the cellulase and the pectinase are added, after enzymolysis and heating, a mixture material is obtained, and then other raw materials are added into the mixture material to process the steamed cake; compared with the prior art, the prepared high-fiber-content sugar-free steamed cake maintains the flavor and appearance of the cake prepared through an original preparation method on the basis of not adding refined sugar components, meanwhile, the prepared high-fiber-content sugar-free steamed cake contains abundant vitamin and mineral substances, the calorie of the steamed cake is greatly reduced, and the steamed cake is applicable to patients suffering from hypertension, hyperlipidemia, hyperglycemia and diabetes.