Abstract: In order to improve the utilization rate of Rosa roxburghii pomace, reduce resource waste and environmental pollution, this study used Rosa roxburghii pomace as raw material and modified dietary fiber (DF) through solid-state fermentation. The ratio of soluble dietary fiber (SDF) to insoluble dietary fiber (IDF) (SDF/IDF) was used as the response value, inoculation amount, fermentation temperature, and fermentation time were used as factors to optimize the optimal fermentation process of Rosa roxburghii pomace using response surface methodology. The structural characteristics and physicochemical properties of dietary fiber before and after fermentation were analyzed. The results showed that the optimal fermentation process for Rosa roxburghii pomace was as follows: Fermentation time of 4 days, temperature of 40 ℃, inoculation amount of 7.5%, SDF/IDF of 14.21%±0.42%. The analysis of physical showed that the water holding capacity, oil holding capacity, and swelling capacity were increased after fermentation compared to before fermentation. The ultrastructural analysis revealed that DF after fermentation exhibited layered morphology, rough surface, and loose structure. The infrared spectrum analysis showed that the intensity of DF absorption peak increased after fermentation, and the overall peak shape and position remain unchanged. The X-ray diffraction spectrum showed that the intensity of diffraction peak weakens after fermentation, and the crystal structure did not changed. The fermentation of Rosa roxburghii pomace by Bacillus subtilis could alter the structure of DF and improve its physicochemical properties.