Double network (DN) hydrogels with high mechanical properties were constructed by acrylamide (AM) and carboxymethyl cellulose (CMC). The mechanism of crosslinking and entangling of the first network polyacrylamide (PAM) and hydrogen bonding of the second network CMC on the mechanical properties of the hydrogel was investigated. The results show that, for the first network, PAM can form a significant entanglement structure at C=10-5 (C=ncrosslinking agent/nmonomer is the crosslinking degree of hydrogel), and can gradually form entanglement structure by sliding molecular chains under stress to achieve energy dissipation. PAM forms a highly crosslinked network at C=10-2, dissipating energy through the breaking of chemical bonds under stress. For the second network, with the mass fraction of CMC in the hydrogel Q=5.0%, significant hydrogen bonds can be formed through freeze-thaw, and the force of the network can be effectively improved, thus improving the mechanical properties of the hydrogel. With C=10-5 and Q=5.0%, the hydrogel stress reaches 0.328 MPa. The high osmotic pressure of CMC will cause the gel to swell and reduce the polymer density. In addition, the introduction of CMC will also affect the entanglement structure of the first network PAM.