Although hydrogel have attracted tremendous attention as antifouling material, it is still challenging to develop an antifouling hydrogel that combines superior mechanical properties with excellent antifouling effect. Here, a high-strength polyvinyl alcohol/sodium alginate double-network (DN) antibacterial and antifouling hydrogel was synthesized by introducing polyhexamethylene biguanide hydrochloride (PHMB) potent fungicide. The as-prepared hydrogel demonstrated high tensile strength (17.23 MPa), excellent anti-protein adhesion ability (0.09 %, anti-diatom adhesion rate), and outstanding antibacterial ability (100 % sterilization rate). The antifouling experiments have verified that DN-PHMB hydrogel remains non-attachment even after >6 months in the actual marine environment. These distinctive capabilities of DN-PHMB hydrogels hold promising candidate for marine antifouling materials.