The work aims to reduce pore size and increase stain resistance of the fiber felts by building superwetting micro-nanostructure on surface of stainless steel fiber felts, so as to achieve efficient separation of emulsified oil. Micron-sized copper particles were deposited on the surface of stainless steel fiber felts in the method of double-anodic electrochemical deposition. Then copper particles were oxidized into Cu(OH)2 nanoneedles with micro-nano structures in the method of electrochemical oxidation. Microstructure, chemical composition, wettability, oil-water separation property of the sample were characterized with scanning electron microscopy, X-ray diffractometer, contact angle meter, oil-water separation test and UV-visible spectrophotometer. After fabrication of micro-nanostructures, wettability of the stainless steel fiber felt transformed into superhydrophilicity (≈0°) and underwater superoleophobicity (161°) from hydrophobicity (135°). Separation efficiency of oil-in-water emulsion could reach up to 99%, even after 8 times of cycling separations. The UV-vis light transmittance could reach over 98% after seperation. Oil droplets in the oil-in-water can be effectively removed. Porous micro-nano composite structures can be successfully constructed on the surface of stainless steel fiber felts in the method of electrodeposition-electrochemical oxidation, and the surface exhibits excellent superhydrophilic/underwater superoleophobic property, which can separate the oil-in-water emulsified oil effectively. After repeated separation, the separation efficiency does not reduce significantly, which proves its excellent stain resistance.