Abstract: The main components of coconut husk fibers was separated by the 1,4-butylene glycol/water system combined with 1-butyl-3-methylimidazolium hydrogen sulfate(Bmim HSO4) as a catalyst, and the cellulose-rich material was subjected to bleaching treatment of sodium chlorite to obtain pure cellulose. Then, the nanocellulose was prepared by acid hydrolysis followed by ultrasonication. The morphological behavior, chemical characterization, crystallinity index, thermostability of nanocellulose were characterized by scanning electron microscopy(SEM), transmission electron microscopy(TEM), Fourier transform infrared spectroscopy(FT-IR), X-ray diffraction(XRD) and thermogravimetric analysis(TG). The effects ofBmim HSO4 on the yield and properties of nanocellulose were investigated. The results showed thatBmim HSO4 the extraction rate of lignin and the disposability of the cellulose, which was beneficial to the preparation of pure cellulose. Nanocellulose from coconut husk fibers still maintain the basic chemical structure and the cellulose I crystalline structure. TheBmim HSO4 increased the mass loss rate of the cellulose, which led to the decrease of the nanocellulose yield. The nanocellulose from Coconut husk fiber based on ionic liquid exhibited an average length of(271±81)nm and a diameter of(6.3±1.8)nm.Bmim HSO4 had no significant effect on the size of diameter(3-9 nm).