A novel superhydrophilic and underwater superoleophobic poly (acrylonitrile-co-methyl acrylate) (P(AN-MA)) microfiltration membrane (MF) was processed. In order to create micro/nanostructured roughness surface and improve the hydrophilicity of the membranes, the thermally induced phase separation (TIPS) method combined with surface hydrolysis reaction method were adopted. The obtained membrane is noted for symmetrical and hierarchical micro/nano-structure with excellent superhydrophilicity and underwater superoleophobicity. It can efficiently separate surfactant-free and surfactant-stabilized oil-in-water emulsions with ultrahigh water fluxes, which is up to 4341 L/m(2) h under a low operating pressure (0.02 MPa). The oil content in the filtrate is below 5 ppm after one time separation, showing significant applicability for energy-saving filtration. In addition, the hydrolyzed PAN-based membrane has superior antifouling property and unconspicuous oil adhesion property, which is noted for excellent reusability. This work provides a simple and green technology to fabricate superhydrophilic PAN-based MF membrane for highly efficient separation of oil-in-water emulsions.