The cylindrical structure finds extensive applications in ocean engineering， where the shedding of wake vortices can generate fluctuating drag that may induce vortex-induced vibrations， which can lead to equipment instability. Reducing the flow drag around the cylinder can help suppress vortex-induced vibrations. In recent years， the use of cactus-inspired riblets and superhydrophobic coatings has emerged as two efficient passive control strategies for drag reduction. This study combines these two methods to conduct experiments on drag reduction in underwater cylindrical flow. The experimental results demonstrate that surface riblets can decrease the drag on the cylinder， and the addition of superhydrophobic surfaces can further enhance drag reduction. Surface riblets extend the recirculation region while superhydrophobic surfaces shorten it. By utilizing Proper Orthogonal Decomposition to compute the phase-averaged flow field， it is found that， compared to hydrophilic cylinders， superhydrophobic surfaces lead to a reduction in the cylinder’s wake shear layer and cause the vortex to form closer to the cylinder， thereby shortening the recirculation region. Overall， the combination of surface riblets and superhydrophobic coatings effectively reduces the flow resistance around the cylinder， offering potential applications in flow control and drag reduction technologies.