Abstract: Nanocellulose is the most abundant biomass resources on the earth, with the advantages of easy degradation, renewable, non-toxic, cheap and easy to obtain.Cellulose nanocrystal (CNC) is one of the main products of nanocellulose. Due to its excellent physical and chemical properties such as high crystallinity, high tensile strength, high stiffness and high specific surface area, it has been widely studied and received extensive attention in recent years. In this paper, the advantages and disadvantages of traditional inorganic acid hydrolysis CNC preparation method and several CNC preparation methods in recent years which are beneficial to save energy consumption and be friendly to environment are compared. The latest research progress of CNC preparation methods and its optimization process is introduced. In addition, the research process of CNC composites in the field of food packaging, retention and filtration, paper performance improvement, immobilized enzyme technology and wastepaper treatment are reviewed. At last, the preparation methods and application research of CNC were discussed, aiming to provide theoretical reference for promoting the production and application scale of CNC and its composites.