The invention relates to application of a microbial fermentation method in co-production of wheat bran oligose and dietary fiber. The invention aims to developed and utilize the wheat bran comprehensively; an efficient biological process route is adopted to deeply processing wheat bran, and the microbial fermentation method is used to prepare wheat bran dietary fiber and functional oligose simultaneously. The microbe used in the method refers to a single strain, pullularia pullulans or mixed strains of aureobasidium pulluans and agrocybe aegerita; in fermentation of wheat bran, substances in the wheat bran, such as starch and protein, can be taken as nutritional ingredients for the growth of microbes, when digesting the substances, the microbes can generate xylanase so as to hydrolyze wheat bran hemicellulose to generate oligose and prepare dietary fiber simultaneously. According to the method, the research and development idea of developing a single product is broken through, the rate of multipurpose utilization of the resource is high, the production costs is low, chemical substance residual does not exist, the environment is not polluted, a new processing technology model of 'ecological, low-carbon and efficient circulating' is formed, and the additional value of the wheat bran product is increased.