Abstract: A miniature amphibious turtle-inspired robot driven by a legged, multi-vectored water-jet composite driving system is proposed for scientific investigation and resource exploration in shallow shoal environment and underwater narrow space.The movement mechanism of the proposed driving system is studied, and bionic crawling and rotation gaits are designed.According to the variable structure characteristics of the proposed driving mechanism, "H", "I"and"X"mode motion are proposed.By modeling the underwater kinematics, a three-dimensional underwater autonomous motion control method is established based on real-time dynamic thrust vector allocation and optimization mechanism.Finally, movement experiments on various terrains prove that the robot prototype has strong adaptability in unstructured shoal environment.Underwater motion control experiments verify the flexibility and feasibility of multi-mode motion.