It is still a challenge to achieve large-area preparation of robust superhydrophobic surfaces with strong mechanical stability. Here, a simple and low-cost method to prepare robust decoupling superhydrophobic coatings on aluminum (Al) alloys substrate has been presented. The superhydrophobicity and robustness of decoupling coatings are realized by structuring surfaces at two different length scales, with nanostructures for superhydrophobicity and microstructures for robustness. This prepared decoupling coating shows promising superhydrophobicity, with water contact angle (CA) of ~158.4° and roll off angle (RA) of ~3°. It also exhibits high repellency for impacting water droplets. Notably, the decoupling coating processes outstanding adhesion strength on the substrate after tape-peeling and cross-cut tests, also with promising wear resistantance after sandpaper abrasion and wear test. The friction coefficient of this decoupling coating is only ~0.2. In addition, the robust decoupling superhydrophobic coating is applied to underwater buoyancy enhancement and fluid resistance reduction (drag reduction rate ~30.09%). This decoupling superhydrophobic coating also displays promising self-cleaning and antifouling properties. Moreover, benefitting from the photocatalytic property of TiO₂, this decoupling coating is also exploited for degrading organics to achieve seawater purification. This obtained decoupling superhydrophobic coating is expected to apply on other solids in marine fields, and the simple and eco-friendly method develops the potential practical application.