Abstract Liquid‐gas phase transition actuation technology, known for its high efficiency, strong output, lightweight flexibility, and environmental friendliness, holds great potential in soft robotics, bioinspired devices, smart sensors, and microelectromechanical systems. However, current technology faces challenges such as low actuation efficiency, insufficient thermal management, and long response times. To address these issues, this study draws inspiration from the unique multiscale fiber structure of foxtail grass and designs a bioinspired liquid‐gas phase transition actuator. The actuator features a spike‐shaped heat exchange structure composed of composite gradient fiber materials, simulating the water absorption, transpiration, and fog collection mechanisms of foxtail grass. This design effectively enhances heat transfer efficiency and optimizes response speed. Bending and linear deformation tests verif the actuator's high responsiveness and adaptability. Additionally, its application in bioinspired underwater pufferfish models and pipeline robots demonstrates high efficiency and stability in dynamic environments. Compared to traditional phase transition actuation technologies, this study significantly improves thermo‐mechanical coupling efficiency, reduces response lag, and overcomes critical limitations of existing technologies. The findings provide new insights and theoretical foundations for the broader application and future development of phase transition actuation technology.