This study investigated the effects of number of times of high-pressure homogenization on the structural properties of insoluble dietary fibres (IDFs) derived from millet bran fermented using Bacillus amylolyticus and the physical stability of aqueous IDF suspensions. Millet bran dietary fibres (DFs) were obtained through liquid-state fermentation (30 ◦C, 180 r/min, 48 h) using Bacillus amylolyticus and further modified via high-pressure homogenization. The physicochemical properties of the homogenised IDFs were evaluated using various techniques, and their structural characteristics were analysed through Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD). The particle size distribution, viscosity, zeta potential, and physical stability of the IDF suspensions in water were evaluated before and after high-pressure homogenization. The water-holding capacity and swelling capacity of the IDFs obtained via millet bran fermentation using Bacillus amylolyticus increased significantly after 0, 5, 10, 15, 20, and 25 cycles of high-pressure homogenization. In particular, the water-holding capacity and swelling capacity increased by 80.5 and 81.84%, respectively, after 25 cycles of high-pressure homogenization compared with those of the untreated IDFs. FTIR spectra revealed that no new chemical functional groups were generated after high-pressure homogenization, but the intensities of certain FTIR peaks were weakened, indicating the partial degradation and rearrangement of lignin and hemicellulose, and decreased ordering degree of the crystalline domains. Combined with the XRD results, it can be inferred that, although the millet bran IDFs exhibited the characteristics of natural type I cellulose, their crystallinity decreased with increasing cycles of high-pressure homogenization. The average particle size of the IDFs in aqueous suspensions gradually decreased with the increase in high-pressure homogenization recirculation, and the absolute zeta potential value increased gradually. When the homogenization recirculation reached 20 times, the aqueous fibre suspension exhibited good physical stability. Moreover, as the cycle number of high-pressure homogenization recirculation increased, the apparent viscosity of the aqueous IDF suspension increased steadily, and all samples exhibited shear-thinning behaviour. High-pressure homogenization can improve the structure and physicochemical properties of IDFs derived from fermented millet bran and enhance the stability of aqueous IDF suspensions.