In response to the requirements of biomimetic swimming propulsion technology, a frog-inspired swimming robot based on a bistable structure is designed. By constructing a linkage-spring-cable composite mechanism, a bistable actuator with rapid energy transition characteristics was proposed. The device utilized an elastic deformation energy storage mechanism of springs to achieve millisecond-level switching between stable states under periodic torque input, generating efficient propulsion through hydrodynamic reaction forces via paddle blades. Subsequently, through ADAMS dynamics simulations and prototype experiments, the influence laws of key parameters such as the paddle blade swing angle amplitude, the spring stiffness, and the spring compression on the response ability and motion performance of the robot were analyzed. Results showed that increasing the stiffness of the main spring k? could enhance the robot's energy storage and release capabilities, and enhance the swing output force, enabling the robot to achieve an average propulsion speed of 43.33 cm/s (1.73 body lengths per second) within 0.3 s after activation. Increasing the compression of the spring k₂ could improve propulsion force, with experiments recording a maximum instantaneous propulsion force of 2.14 N (2.58 times body weight). Tests demonstrated that when the actuation cycle of the bistable actuator was 0.5 s, the robot achieved a stable swimming speed of 22.5 cm/s. The designed bistable actuator provides a new paradigm for high-power-density actuation in biomimetic underwater robots, enhancing the application potential of robots in disaster rescue and ecological monitoring fields.