Molecular dynamics simulations were performed to examine the mechanical properties of poly(carboxybetaine methacrylate) (pCBMA) hydrogels. pCBMA hydrogels with additional hydroxyl groups as physical cross-linkers (OH-pCBMA hydrogels) were studied for comparison. Results show that OH-pCBMA hydrogels have higher elastic modulus than pCBMA hydrogels. This improvement can be explained by hydrogen bond formation between hydroxyl groups and carboxylate groups in the OH-pCBMA hydrogel, which result in an enhanced polymer network within the hydrogel. The enhancement of the polymer work is also suggested by a smaller value of root-mean-square deviation of zwitterionic side chain pairs in the OH-pCBMA hydrogel than that in the pCBMA hydrogel. Additionally, the presence of hydrogen bonds leads to a lower equilibrium water content for the OH-pCBMA hydrogel compared to the pCBMA hydrogel, which is another reason for the greater mechanical modulus of the OH-pCBMA hydrogel.