The development of membranes with a superior antifouling property and high-permeation flux is extensively considered but still a challenge for handling emulsified oil foulants in wastewater. Herein, a zwitterionic nanohydrogel-grafted PVDF (ZNG-g-PVDF) nanofibrous membrane was fabricated via a simple surface activation and amide reaction. By tailoring the parameters for electrospinning, PAA-g-PVDF nanofibrous membranes with interpenetrated nanofibers and microsphere structure were formed, and the membrane surface was endowed with high roughness on the micrometer scale. Combined with the strong hydration ability of the grafted zwitterionic nanohydrogels, the obtained ZNG-g-PVDF nano fibrous membrane exhibited a superhydrophilic property and nearly zero adhesion to crude oil under water. It thus showed an extremely high removal efficiency (similar to 98.7%) for gravity-driven separation of the crude oil-in-water emulsion. Both the water-permeating flux and oil content in the collected filtrate (lower than 13 ppm) showed little change during 10 cycles of the filtration experiment, indicating superior crude oil foulant repellency performance of the ZNG-g-PVDF nanofibrous membrane. Considering the high energy saving of the gravity-driven separation process, this novel ZNG-g-PVDF nanofibrous membrane possesses broad applications in the field of emulsified crude oil foulant cleanup in an aquatic environment.