This paper addresses the limitations of traditional water quality detection equipment in aquaculture, such as restricted detection range and insufficient depth, by designing a water quality detection robot and conducting structural dynamics and fluid dynamics analyses to verify the feasibility of the proposed design. First, the robot’s structural design and modeling were carried out, and the electronic cabin was subjected to static strength verification using the finite element method. Second, based on CFD, RANS and RNG k-ε turbulence models were used to analyze the robot's straight-line motion performance at speeds ranging from 0.2 to 1.0 m/s. Finally, overlapping grid technology was applied to explore the robot’s variable-speed motion characteristics. The results show that at a depth of 100 meters, the maximum equivalent stress in the electronic cabin is 50.70 MPa, with a maximum deformation of 0.0763 mm, which meets the pressure resistance requirements. Under straight-line motion, the hydrodynamic coefficients (、、、 and ) were −34.75, −37.54, −82.81, −71.16, and −93.47, respectively. In the variable-speed motion state, the corresponding inertia hydrodynamic coefficients (、 and ) were −7.32, −24.25, and −22.53, respectively. This study not only provides a novel equipment with underwater mobile detection system capable of full-range water quality monitoring,  but also offers data support for the structural optimization and motion control strategies, advancing its practical application in the field of water quality detection.