We design a novel underwater accompanying robot capable of collaborating with divers for joint operations to improve the efficiency and safety coefficient of underwater operations for divers by studying the impact of speed and drift angles on its hydrodynamic performance under various underwater conditions. Utilizing the computational fluid dynamics (CFD) method, applying the Realizable k − ε turbulence model, and incorporating standard wall functions for near-wall regions, Fluent software is employed to simulate fluid dynamics and solve hydrodynamic parameters for various underwater conditions and postures. Research findings indicate that conditions of horizontal straight navigation and vertical ascent/descent, pressure drag, and viscous drag on the robot exhibit a positive correlation with velocity. Experiencing variations in drift angle, the robot’s longitudinal movement is not significantly altered during horizontal maneuvering and remains consistent under the same velocity. Conversely, later resistance distinctly increases with larger drift angles. This study can offer valuable reference and insights for subsequent research on underwater accompanying robots.