Injectable hydrogel adhesives integrating both rapid adhesion to wet tissues and anti‐swelling in humid environments are highly desired for fast hemostasis and wound sealing in surgical applications. Herein, utilizing the synergistic effect of thermo‐sensitive shrinkable nano‐micelle gelators and small molecular adhesive moieties, an injectable hydrogel with rapid‐adhesion and anti‐swelling properties (RAAS hydrogel) is fabricated. The RAAS hydrogel can undergo ultrafast gelation to achieve wet adhesion within 2 s of ultraviolet illumination and exhibit an outstanding anti‐swelling performance with non‐expansion of volume during the whole degradation process. It also presents good biocompatibility and low risk of hemolysis. Its fast hemostasis is demonstrated in diverse hemorrhage models with injuries in the liver, artery, heart, cranial vessel, and brain cortex in small animals. Importantly, its volume stability in humid internal environment can maintain the strong adhesion strength and avoid compression injury to spinal cord when applied for dura sealing. These data suggest that the injectable RAAS hydrogel holds potential for the applications of fast hemostasis and wound sealing with the benefits of stable adhesion and reducing the risk of tissue compression injury. [ABSTRACT FROM AUTHOR]