CMC applying in coating size can well control and adjust the rheological and dispersing properties, raise the solid content, and increase water retention and lubricating effects of coatings. Improve quality of coatings and prolong operation life of slicker. Make finished paper with good brightness and ink absorption effect. Promote better fiber refinement process. Shorten pulping time. Adjust electric potential in pulp. Disperse fiber. Improve production capacity of paper machine. During size on the surface of paper, can reduce blowholes of paper, increase gease-proof effect. Can improve brightness, surface tension, sizing force, strength of stiffness and smoothness of paper. Reduce surface picking and raise the printing quality.