Agriculture wastes-- wheat straw is used as raw material to take place of cotton and wood pulp in this research. In order to separating of the crude cellulose, non-polluting ethanol/acetic acid binary solvent system is utilized to dissolve lignin. Then pure cellulose is obtained by refining processing. Finally, microcrystalline cellulose is obtained by acid hydrolysis, grinding and the subsequent process. The paper focuses on the effect of the dosage of acetic acid in the binary solvent system on separating efficiency of wheat straw cellulose, and analyzing the effects of acetic acid dosage on kappa number, yield, α-cellulose content and crystallinity of the wheat straw crude cellulose. The results indicated that acetic acid can promote the removal of lignin and hemicellulose degradation, and is conducive to improve the purity of crude fiber. The lignin removed mainly adsorbed and deposited onto the surface of crude cellulose. The optimum dosage of acetic acid in the thermal decomposition system of wheat straw is 2%. Under the optimum condition, the crystallinity of crude cellulose is the highest, the yield and α-cellulose content are both rather high, but a low Kappa number.