Biocompatible polydopamine-polyacrylamide (PDA-PAM) hydrogel has good self-healing performance. However, there is a trade-off between the self-healing ability and the mechanical strength. Excellent self-healing often results in the poor mechanical strength, which limits the application in load-bearing field. Here, we successfully prepare PDA-PAM hydrogels with improved strength and good self-healing properties simultaneously. By adjusting the pH and ammonium persulfate (APS) content of the hydrogel solution to promote dopamine (DA) polymerization, PDA-PAM hydrogel with a high content of polydopamine (PDA) is developed, which demonstrates excellent self-healing properties and mechanical strength. In particular, the PDA-PAM hydrogel with high PDA content (DA/AM = 5%) has a tensile strength of 16 kPa and the tensile strength spontaneously recovers 96% in 2 h after the tensile fracture. The obtained hydrogel also displays good biocompatibility.