A superhydrophilic-underwater superoleophobic stainless steel mesh (SSM-PDA-SiO2) was prepared using a stepwise deposition and in-situ growth method for gravity-driven oil-water separation. Nano-sized silica (SiO2) was grown in situ on a polydopamine (PDA) modified stainless steel mesh to impart superhydrophilic-underwater superoleophobic properties. The chemical composition, morphology, and wettability of the modified stainless steel mesh were characterized using techniques such as FT-IR, XRD, TG, SEM, and contact angle measurement. The experimental results showed that the SSM-PDA-SiO2 obtained after eight hours of silica sol addition exhibited the highest underwater contact angle (159.6°) and the lowest rolling angle (5°), demonstrating superhydrophilic-underwater superoleophobic properties. The modified stainless steel mesh achieved an initial separation flux of 40165 Lm-2h-1 with a separation efficiency of 99.3%. Even after 50 separation cycles, it still maintained a flux of 17728 Lm-2h-1 and a separation efficiency of 98%, indicating good recyclability. Additionally, after 35 cycles of sandpaper abrasion, the modified stainless steel mesh retained a separation efficiency of over 98%, demonstrating good mechanical stability.