A novel mussel-inspired polyurethane underwater adhesive (PUWA) with fast bonding and hemostatic properties has been developed. The PUWA is created through an injectable two-component curing process of component A (biocompatible polyurethane prepolymer) and component B (dopamine-modified lysine derivatives: chain extender-LDA and crosslinker-L3DA). The adhesive cures quickly and firmly underwater, achieving a bonding strength of 40 kPa on pork skin and a burst pressure of 394 mmHg. It exhibits robust adhesion in hostile environments, including acid, alkali, and saline solutions. The PUWA demonstrates excellent biocompatibility and hemostatic performance, effectively sealing wounds and promoting healing. It can bond diverse substrates rapidly and strongly, making it suitable for biomedical and industrial applications. The PUWA's isocyanate esterification process does not require organic solvents or external stimuli, enabling fast curing. The adhesive's catechol groups interact with substrates to form physical or chemical interactions, enhancing adhesion. The PUWA shows strong adhesion to various materials, including titanium, stainless steel, ceramic, polyamide, polyvinyl chloride, and polypropylene. It also exhibits good adhesion to pork skin, with adhesion strength more than ten times that of commercial fibrin glue. The PUWA's biocompatibility was evaluated using cell viability tests, hemolysis experiments, and subcutaneous implantation, showing no significant toxicity or inflammation. The PUWA's hemostatic properties were tested using a mouse liver hemorrhage model, demonstrating effective wound sealing and blood clot formation. In vivo wound healing tests showed that PUWA-1 significantly improved wound closure and repair compared to other materials. The PUWA's degradation behavior was observed in vitro and in vivo, showing controlled weight loss and surface changes over time. The PUWA's hemostatic performance was further confirmed through blood clotting index (BCI) tests, showing rapid blood coagulation. The PUWA's excellent adhesion, biocompatibility, and hemostatic properties make it a promising candidate for wound closure and repair in biomedical applications.A novel mussel-inspired polyurethane underwater adhesive (PUWA) with fast bonding and hemostatic properties has been developed. The PUWA is created through an injectable two-component curing process of component A (biocompatible polyurethane prepolymer) and component B (dopamine-modified lysine derivatives: chain extender-LDA and crosslinker-L3DA). The adhesive cures quickly and firmly underwater, achieving a bonding strength of 40 kPa on pork skin and a burst pressure of 394 mmHg. It exhibits robust adhesion in hostile environments, including acid, alkali, and saline solutions. The PUWA demonstrates excellent biocompatibility and hemostatic performance, effectively sealing wounds and promoting healing. It can bond diverse substrates rapidly and strongly, making it suitable for biomedical and industrial applications. The PUWA's isocyanate esterification process does not require organic solvents or external stimuli, enabling fast curing. The adhesive's catechol groups interact with substrates to form physical or chemical interactions, enhancing adhesion. The PUWA shows strong adhesion to various materials, including titanium, stainless steel, ceramic, polyamide, polyvinyl chloride, and polypropylene. It also exhibits good adhesion to pork skin, with adhesion strength more than ten times that of commercial fibrin glue. The PUWA's biocompatibility was evaluated using cell viability tests, hemolysis experiments, and subcutaneous implantation, showing no significant toxicity or inflammation. The PUWA's hemostatic properties were tested using a mouse liver hemorrhage model, demonstrating effective wound sealing and blood clot formation. In vivo wound healing tests showed that PUWA-1 significantly improved wound closure and repair compared to other materials. The PUWA's degradation behavior was observed in vitro and in vivo, showing controlled weight loss and surface changes over time. The PUWA's hemostatic performance was further confirmed through blood clotting index (BCI) tests, showing rapid blood coagulation. The PUWA's excellent adhesion, biocompatibility, and hemostatic properties make it a promising candidate for wound closure and repair in biomedical applications.