In this study, a simple electrospinning method was employed for the fabrication of a durable and renewable cellulose/polyacrylonitrile (cellulose/PAN) composite nanofiber by alternatively piled one over other as stacking. The stacking layers of cellulose/PAN composite fiber was subjected to the hot roller press at 80 degrees C to enhance the firm attachment of fibers. The hydrophilic composite fiber was fabricated for oil-in-water mixture separation in harsh conditions of different pH. The fibers were characterized by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), and thermal stability was monitored by TGA analysis. The tensile stress and the surface wetting behavior were greatly improved for cellulose/PAN composite fiber. The different oils like n-hexane, diesel oil, and toluene were used to prepare oil-in-water mixture solutions. The hydrophilic composite fiber served as a substrate to ensure the high water permeation flux and high separation efficiency with excellent stability and durability. This work projects an easy cost-effective fabrication method of composite fiber for on-demand oil-in-water separation process having good application in adverse situations with excellent recyclability and the maximum separation efficiency up to 97.31%.