Air–water trans-media vehicle is a special type of aircraft that possesses an operational capability both in the air and under the water. It not only incorporates the individual performance advantages of underwater vehicles and aerial vehicles but also breaks through the physical barriers between water and air domains. Thus, this type of vehicle holds great potential for both civil and military applications. Many existing researches related to cross-media vehicles have adopted multi-rotor configuration designs, which are limited by their sizes in future practical applications. This paper proposes a blended wing-body (BWB) configuration design for an air–water trans-media vehicle. This design eliminates the need to alter its geometric shape and achieves both aerial and underwater flight performance with an integrated configuration. Computational Fluid Dynamics (CFD) is employed to investigate the fluid dynamic performance of the vehicle in both the air and underwater environments. The results indicate that, in underwater navigation, the vehicle can maintain low drag and a high lift-to-drag ratio within a small range of pitch angles, and in the air, it possesses a large stalling angle of attack (AOA) and a high lift-to-drag ratio.