The microwave was used to modify the dietary fibers (DFs) in sweet potato pomace, apple pomace, and soybean pomace. The changes in the structural properties of three kinds of DFs by microwave were investigated by scanning electron microscopy, X-ray diffraction and thermogravimetric analysis. Moreover, the functional properties, including water holding capacity, oil holding capacity, cholesterol adsorption capacity and nitrite ions adsorption capacity, were evaluated in this study. The results showed that microwave was an excellent modification method that could expose the accessibility margin, increase crystallinity, strengthen thermal stability, and improve the functional properties of three dietary fibers to varying degrees. In addition, after modification, the soluble dietary fiber mass fractions of the three dietary fibers were increased by 63.11%, 4.51% and 358.79%, respectively, which was not positively correlated with the improvement of functional properties. The improvement of functional properties was related to the mass fraction of SDF, but the exposure of the accessibility margin on IDF also promoted an important influence for the improvement of DFs functional properties.