Abstract: 【Objective】The model of the relationship between microfibril length and microfibril angle in S₂ fiber layer was developed based on the microstructure characteristics of plant cell walls, which can be used to estimate the fiber length for the preparation of nanofibers. 【Method】The fibers were cut to the range of the calculated length quickly by the free beating and crushing by the subsequent alkaline treatment(pH = 7.5). The morphology and structure changes were examined using a combination of AFM and TEM. 【Result】The water retention value(r(WRV))increased drastically from 125.6% to 319.3% for the fibers that had a length ranging from 0.41-0.64 mm. The rigid structure of fibers was easily destroyed due to the generating of longitudinal cracking. The results also demonstrated that it would be much easier for Na⁺ ion to penetrate the internal layers of fibers from fiber ends and surface cracks, resulting in swelling fibers, removing P and S₁ layers of the fibers’walls, and decreasing fibers’bonding effectively. From the characterization results, the crystallinity of the fibers was 72%-73% and the activation energy of pyrolysis was 75.02-76.93 kJ/mol in the early stage of compression(r(WRV)=125.6%). With the increase of the compressive strength(r(WRV)=319.3%), the crystallinity of the fibers decreased to 45% and the activation energy of pyrolysis decreased to 37.78 kJ/mol. This further confirmed that the fiber with a certain strength crushing treatment can effectively weaken the binding force between the fiber microfibril layers. 【Conclusion】The fibers originated from different types of raw materials and possessed different morphologies can be cut into short fibers with an appropriate length, thus facilitating the crush, swell and micro-miniaturized process.