Since oily wastewater has serious harm to the environment and human health, a green paper-based material with underwater superoleophobicity, high wet strength and high flux was developed for the efficient oil–water emulsion separation. A series of key steps, including fiber beating, citric acid (CA) crosslinking, and dielectric barrier discharges (DBD) plasma treatment, were successfully adopted to control the pore size in micron scale, enhance the wet strength, and improve the underwater superoleophobicity, respectively. Moreover, DBD plasma treatment led to a significant increase in the porosity while maintaining the pore size, which is beneficial to improve the flux with high separation efficiency. The maximum porosity and flux can reach 59.7% and 106 L/m2∙h, respectively. The separation efficiency of emulsified oil is high up to 99.60% even when the average droplet size is as low as 0.98 µm. This high-efficiency, low-cost, environmentally-friendly, and recyclable paper-based separation material possesses potential applications in oily wastewater treatment.