A series of new zwitterionic N-carboxymethyl-N,N-dimethyl-N-allylammonium (CDMA)/acrylic acid (AA) copolymer hydrogels with different contents of anionic and cationic groups were prepared by aqueous polymerization to investigate their swelling behaviors. Various factors, including the solution pH, the various salt solution, temperature, were studied. The dynamics parameters were also calculated. The swelling capacity, as well as salt-tolerant ability increases with increasing N content in the dilute solution of salts. The hydrogel with 2.43% N and 49.54% COOH reaches 773 g/g swelling capacity. CDMA/AA copolymer gel can improve the pullulating rate of wheat remarkably, which makes them good candidates for considering as potential soil-improvement agent.