Repairing Achilles tendon has emerged as a long-standing challenge in the orthopaedic surgeries. Although suture is the gold standard for re-attaching and repairing the fractured Achilles tendons in clinical surgeries, it is still subjected to numerous adverse side-effects, including chronic inflammatory, tendon tissue re-rupture, scar formation, and post-surgical peritendinous adhesion. In this work, we develop a class of hydrogel bioadhesives with tailored nanoscale phase separation for Achilles tendon repairing. To address the existing limitations of sutures, our hydrogel bioadhesives encompass three core functionalities: (i) instant and tough adhesion to Achilles tendon tissues, (ii) extraordinary long-term adhesion robustness under wet and dynamic in vivo conditions, and (iii) anti-postsurgical peritendinous adhesion. Combining our hydrogel bioadhesives with sutures, such kind of integrated approach enables a conformable yet robust biointerface with the tendon tissues, and prevents the fibroblast migration and formation of connective tissues, thus facilitating the tendon repairing. The hydrogel bioadhesives reported here open up new opportunities for the repairing of fractured Achilles tendons in diverse and complicated clinical scenarios.