Most self-healing hydrogels always exhibited poor mechanical property which largely limited the applications in many fields. In this work, g-C3N4 nanosheets were introduced to the PVA-borax hydrogel to reinforce the network without sacrificing the self-healing ability. The obtained hydrogel displayed remarkable tensile strength (0.98 MPa), Young’s modulus (1.54 MPa) and toughness (4.43 MJ m−3), of which the self-healing efficiency reached to 99 % in 10 min at room temperature. Overall, the strategy proposed in this work provides a simple, operatable and moderate approach to hydrogel with both excellent mechanical property and self-healing ability.