Abstract: Objective Design a morphable underwater robot for deep-sea (up to 1000m) missions, integrating cruising and intervention (grasping, marking, panel operation) capabilities in a single platform. Methods The robot's overall design, including the morphing mechanism and pressure hull, was established and verified using Finite Element Analysis. Performance was analyzed across two modes: high endurance/maneuverability in cruising mode, and stability/workspace in intervention mode. Performance was then validated via simulation. Results The robot is capable of 1000m cruising and intervention. The maximum restoring moment in intervention mode increased by 202.1% over cruising mode. Low drag in cruising mode and high stability in intervention mode were confirmed. Conclusion The morphable underwater robot design successfully achieves multi-task capability in the deep sea, solving the existing challenge of single-dive robots being unable to perform both survey and intervention.