An aquatic Unmanned Aerial Vehicle (AquaUAV) is a hybrid underwater-aerial vehicle which can fly in the air and navigate in the water. The AquaUAV is a unique class of vehicle that is of particular interest for applications, which demand task execution in both aerial and underwater environments. Survival in the two contradictory fluids needs particular shape, fuselage and wing structure, propulsion. However, to address challenges such as difficulties in high-speed plunge diving, and stable submergence, the AquaUAV of morphing flying-wings is proposed to transform the shape actively to obtain high efficient performance during plunge diving processes in this paper, where the diving simulation (DS) method are established for the morphing AquaUAV, which includes that the Detached Eddy Simulation (DES) with κ-ω SST indicates complicated flow characteristics during the diving, the volume of fluid (VOF) captures the gas-fluid interface, furthermore reveals the cavitation effect in the diving process. From the results, the AquaUAV achieves efficient transitions in the plunge diving between the air and water and stable submergences in the water, which were solved using the nonlinear multiphase flow dynamics and ventilated cavity. Finally, the cross-medium transition efficiency and submergence stability are improved significantly by the morphing flying-wings.