Abstract: A choline chloride-urea(molar ratio of 1:2) based deep eutectic solvent(DES) system was used as a non-hydrolytic pretreatment media to prepare the cellulose nanofibrils(CNF) from bleached kraft poplar pulp by using microfluidizer. The properties of CNF were characterized by elemental analysis, scanning electron microscope(SEM), Fourier transform infrared spectroscopy(FT-IR), thermogravimetric analysis and X-ray diffraction analysis. Furthermore, the polymerization degree(D_P) of CNF and the energy consumption were calculated. The results showed that DES pretreatment could promote the swelling of pulp fibers, which was beneficial to fibrillation during the microfluidization process. The microfluidization treatment, was performed 15 times. It was found that compared with the energy consumption(4.35×10⁷ kW·h/t) of raw materials without DES pretreatment, the energy consumption(2.44×10⁷ kW·h/t) of raw materials with DES pretreatment decreased by 43.91%. whereas the crystallinity indexes(I_Cr) of CNF prepared before and after pretreatment were 54% and 44%, respectively. However, DES pretreatment had no obvious effect on the polymerization degree of fiber raw materials. DES pretreatment also reduced the thermal stability of CNF. The increase of homogenization times could promote the fibrillation of fibers, and reduce the crystallinity and polymerization degree of cellulose at the same time. FT-IR analysis showed that choline cations interacted with anionic groups of cellulose fibers through static electricity during DES pretreatment. Elemental analysis showed that nitrogen-containing residues remained in CNFs.