The Amphibious Unmanned Aerial Vehicle （AquaUAV）， capable of operating in both aerial and underwater modes， holds great potential for applications in civilian and military domains. Its uses span from marine environmental surveys to island and reef patrol monitoring， showcasing its expansive development possibilities. In order to enable loading and launching of the vehicle from an underwater platform， this article introduces an amphibious drone called “ABDragon”， which features three operational modes： shallow seabed submersion， water surface floating， and aerial flight. To begin with the overall design， ABDragon employs coaxial propulsion， a high aspect ratio fuselage layout， and modular cabin design. By incorporating a depth control cabin， the relationship between gravity and buoyancy can be adjusted， facilitating submersion and surfacing in water. Thoughtful cabin positioning enhances the system’s hydrodynamic stability， ensuring stable posture throughout the entire process of submersion and floating underwater. Furthermore， modeling of flight dynamics and analysis of underwater stability of ABDragon are conducted. Based on the L1 adaptive control method， the flight control laws are developed. Ultimately， a prototype of ABDragon is manufactured， and is validated in multiple modes including submersion-resurfacing， aerial flight， and cross-medium operations. The experiments show that ABDragon， capable of completing cross-domain operations within 2 s， attains a flight altitude control precision of 8 cm and an angular control precision of 2° and maintains a consistently stable vertical posture during underwater operation， thereby validating the effectiveness of the design.