Natural and synthetic dry strength agents are mostly hydrophilic polymers, these polymers are dispersed in the fiber between the increase in the number of bond between the fibers, so as to achieve the purpose of improving the strength of paper. Most dry strength agents contain cationic groups attached to the main chain ring, thus increasing the binding force between the polymer and the fiber and improving the retention of the polymer. Commonly used dry strength agents are natural polymers such as starch and its modified products (such as cationic starch, anionic starch), synthetic polymers such as polyacrylamide, glyoxal polyacrylamide and polyvinyl alcohol, and other water-soluble natural products Type dry strength agent. In most cases, only the addition of 0.1% to 0.35% of the mass of the substance can achieve effective dry strength effect. China's anionic polyacrylamide and modified starch-based.