Abstract: The rice straw was pretreated by choline chloride/urea deep eutectic solvent(DES) system, and the pretreated straw fiber was dissociated by mechanical homogenization treatment. With the DES addition of 1.5%, 2.5%, 3.5% and 4.5% of the straw mass, the prepared dissociated fiber slurries were labeled as DES-1.5%, DES-2.5%, DES-3.5% and DES-4.5%, respectively, while the sample without DES treatment was used as the control(CK). The properties of the dissociated fibers were characterized by Fourier transform infrared spectroscopy(FT-IR), X-ray diffraction(XRD), scanning electron microscopy(SEM) and fluorescence microscopy. The chemical composition of the dissociated fibers treated by different methods was analyzed by NREL method, and the mechanical energy consumption of the disc mill and the film-forming mechanical properties of the dissociated fibers were studied. The results showed that the homogenization pretreatment of DES system combined with disc grinding machine could destroy the connection of LCC through the competition of hydrogen bonds, thus promoting the dissociation of straw fibers and facilitating the fibrillation of fibers. Compared with CK, when the addition amount of DES was 3.5%, the microfibril angle and crystallinity increased from 35.84° and 41.3% to 47.61° and 50.1%, respectively, in addition to a lignin content decrease by 5.3 percentage points. Moreover, the fracture of the surface layer of rice straw fiber increased, and the energy consumption of disc milling decreased by 160 kW·h/t. The straw fiber mulch prepared under this condition had the best weighted mechanical properties. The results of fluorescence microscopy showed that DES pretreatment could accelerate the migration and dissolution of lignin to the surface of straw fiber.