Poly(methyl methacrylate-co-glycidyl methacrylate) P(MMA-co-GMA) and polyethyleneimine (PEI) were blended with poly(vinylidene fluoride) (PVDF) via phase separation and allowed to undergo in situ crosslinking copolymerization to produce a superhydrophilic and underwater superoleophobic membrane for oil/water emulsion separation. The P(MMA-co-GMA) copolymer served as a crosslinker for the crosslinking copolymerization of the hydrophilic PEI polymer. Both of these polymers were chosen to reduce losses of the hydrophilic polymers typically encountered during membrane preparation. The successful preparation of these coatings was demonstrated by TGA, SEM, ATR-FTIR and XPS characterization. Blending with the hydrophilic components significantly improved the hydrophilicity of the blend PVDF membranes. The membrane became superhydrophilic and superoleophobic underwater while also exhibiting underwater anti-oil-fouling performance. The blend PVDF membrane can intercept the oil droplets while allowing water to pass through, exhibiting excellent performance for oil/water emulsion separations. In addition, the blend PVDF membrane withstands repeated use and long-term operation due to the in situ crosslinking strategy employed.