Janus bio-adhesive hydrogels are promising for preventing postoperative tissue adhesion. However, integrating adhesive and non-adhesive interfaces involves multiple processes, posing challenges in meeting complex clinical demands. Herein, a Janus chitosan (CS) and poly(ethylene glycol) methacrylate (PEGMA) hydrogel (CS/PEG hydrogel) was developed via a one-pot phase separation polymerization process. This phase separation was driven by simultaneous hydrogelation upon ultraviolet light irradiation on the top and heating at the bottom of the precursor solution. The light-induced surface (denoted as LIS) was rich in CS, whereas the heat-induced surface (denoted as HIS) contained a large amount of PEGMA. Owing to the large amount of poly(ethylene) glycol (PEG) present, non-adhesive HIS exhibited a pore size of 235.0 ± 11.3 μm, permitting mature vascularization. The adhesive LIS containing CS maximized the adhesiveness of the untreated wound, reaching 94.1 ± 3.3 J·m⁻². The three-dimensional crosslinked network ensured adequate strength to match the mechanical properties of the skin, with the tensile modulus and compressive modulus reaching 32.2 kPa and 121.9 kPa, respectively. In vitro and in vivo experiments confirmed that this Janus hydrogel achieved nearly complete wound closure (>96%) within 14 days by promoting antibacterial activity, anti-inflammatory effects, epithelialization, angiogenesis, and collagen deposition. The straightforward one-step integration of biocompatible CS and PEG to produce asymmetric hydrogels creates new opportunities for manufacturing adhesive dressings in advanced tissue repair scenarios.