Underwater vehicles typically rely on batteries or other energy sources for operation, where drag reduction can significantly lower energy consumption and extend operational endurance. Inspired by the skin structure of loaches, a flexible structure with scales and mucus pores was designed. First, numerical simulations were conducted. To accurately demonstrate the interaction between the flexible flow field and the fluid flow field and to capture the movement boundaries of the plates, a bidirectional fluid–structure interaction simulation method was used. The numerical results indicate that the flexible structure has a positive effect on drag reduction. In channel experiments, the drag reduction effects of flexible and non-flexible structures were compared. Both showed optimal drag reduction at a water flow speed of 2 m/s and mucus flow speed of 0.1 m/s. The maximum drag reduction rate for the flexible structure was 28.5%, compared to 22.8% for the non-flexible structure. This difference is attributed to the flexible structure altering the flow pattern of the near-wall boundary layer, reducing the velocity gradient of the boundary layer, and increasing its thickness. The findings of this study can provide guidance for future research on flexible surface drag reduction technologies.