<p>A transmedia vehicle is a new concept vehicle that can work underwater and in the air simultaneously. To ensure high-speed and long-distance motility in different media, turbine performance is optimized and investigated in this paper from several perspectives. The unsteady calculation results and 3D optimization of the turbine were analyzed via the CFD method. The results indicate that the stagger angle has a significant effect on the flow separation phenomenon in the blade passage. The scarfed angle of the nozzle affects the force magnitude of the rotors mainly by changing the inlet airflow angle. At blade stagger and nozzle scarfed angles of 18° and 13°, respectively, the efficiency of this partially admitted turbine is greatly improved. After the nozzle profile is improved according to the method of characteristics, the flow direction is changed by improving the development direction of the expansion wave at the nozzle outlet. In underwater mode, the turbine efficiency is increased by 7.5%. In air mode, the expansion ratio of the turbine decreases as the rotational speed increases, increasing flow separation losses inside the nozzle and expansion losses at the turbine outlet. The partial admission degree of the turbine considerably affects efficiency. Adopting the arrangement of four nozzles in air mode improves the turbine efficiency by 4%.</p>