Abstract: Objectives To investigate the motion characteristics and flow field properties of trans-medium submersibles during underwater straight navigation and turning maneuvers. Methods Based on the numerical simulation technology of computational fluid dynamics, the VOF multiphase flow model and the SST k-ω turbulence model are used to establish the numerical computation model of the underwater navigation of the transmedia submersibles. The validity of the numerical method was verified by comparing the total drag results from experiments on the submarine model (DARPA Suboff) at different speeds with the numerical calculation results. On this base, numerical simulations and analyses of the underwater straight navigation and turning maneuvers of the trans-medium submersible were conducted, focusing on the effects of conduit propeller rotation speed and tail fin deflection angle on the underwater straight navigation and turning performance of the submersible. Results The results indicated that during underwater straight navigation, the speed of the trans-medium submersible exhibited an approximately linear relationship with the propeller rotation speed, and the negative pitch moment increased with propeller speed while its absolute value gradually decreased, suggesting that stable attitude can be maintained during high-speed navigation. Additionally, the propeller speed had little effect on the surface pressure coefficient distribution and flow field structure. In the underwater turning phase, the turning radius was primarily influenced by the tail fin deflection angle and was almost unaffected by the propeller speed; the turning radius decreased as the tail fin deflection angle increased, with a gradually slowing reduction trend. The turning speed of the trans-medium submersible was influenced by both the propeller speed and the tail fin deflection angle, with the thrust from both sides' propellers increasing in tandem with both parameters, and the thrust from the outer propeller in the turn consistently exceeding that of the inner propeller, with the difference also increasing with the tail fin deflection angle. Furthermore, during the turning motion, the pressure distribution on the surface of the trans-medium submersible exhibited distinct asymmetrical characteristics due to the deflection of the tail fin, with this asymmetry becoming more pronounced as the tail fin deflection angle increased, closely related to the asymmetric flow around the submersible. Conclusions This study can provide a reference for transmedia submersibles configuration design and underwater navigation performance analysis.