This paper proposes a novel underwater robotic system based on bionic tail-swimming and dual-independent propulsion, integrating oscillatory tail-fin propulsion with propeller-driven thrust for enhanced maneuverability and efficiency. Conventional underwater robots often suffer from excessive noise, limited agility, and a suboptimal performance in single-propulsion modes. To overcome these challenges, a modular biomimetic design is introduced, featuring a segmented structure comprising a bow section, control and navigation module, battery compartment, and tail-driven propulsion unit. Two independently sealed motor systems enable seamless switching between bio-inspired undulatory motion and high-speed propeller-based cruising. Hydrodynamic simulations reveal that the optimal tail-fin oscillation amplitude ranges between 30° and 40° for maximum efficiency under a fixed cycle. Furthermore, kinematic analysis demonstrates that propulsion speed increases with higher tail-fin oscillation frequency at a given amplitude, leading to the establishment of linear thrust-frequency and speed-frequency models. These findings provide a theoretical foundation for optimizing bionic propulsion parameters in hybrid underwater robotic systems.