Crystal cellulose that biosynthesized by the cellulose synthetase (CesA), is the structural framework and the most important components of the cell wall of higher plants. During the process of biological evolution, CesA aggregates on the plasma membrane and forms super-molecular terminal complexes (TCs) which have the two types of arrangement: TCs and rosettes TCs, synthesizing Ⅰα and Ⅰβ crystal cellulose, respectively. Due to the unbranched structure, the adjacent cellulose chains can quickly stack side by side to form microfibre under the hydrogen bonds and Van der Waals' force (VDW). As a result, tightly crystal super-molecular structure of microfibre work as a natural barrier and makes it become an obstacle to the degradation which is known as biomass recalcitrance. However, concentrated acids and ionic liquids can diffuse among the microfibre efficiently and break β-1, 4-glucosidic bonds and hydrogen bonds, and eventually destroy the crystal structure of cellulose. Crystal cellulose can also be degraded by biological enzymes, which is quite different from chemical treatments which both require extremely acting conditions. Cellulases can hydrolysis crystal cellulose at room temperature, but only the certain surface of microfibre can be interacted with celluases, so the accessibility of cellulose surface further reduce the efficiency of hydrolysis. Therefore, the combination of physical and chemical pretreatments can break the biomass recalcitrance and then cellulases can spread into microfibre which resulting in the specific binding rates of enzyme-substrate increased. Finally, it can realize the degradation and conversion of natural crystal cellulose with low-cost and green high-efficiency.