Abstract: Facing increasingly stringent volatile organic compound (VOCs) emission standards, the conventional"adsorption-absorption "process for oil vapor recovery in existing oil depots no longer meets advanced treatment requirements. This study focuses on a refined oil storage and transportation depot, proposing and implementing a retrofitted" adsorption-absorption-membrane "hybrid process. An induced draft fan was added to the vapor collection system to create a slight negative pressure, and a refining unit based on a poly (octylmethylsiloxane)/polyacrylonitrile (POMS/PAN) composite membrane was integrated at the end of the original process, enabling deep recovery and ultra-low oil vapor emissions. Engineering results indicated that the hybrid process consistently reduced non-methane total hydrocarbon (NMHC) emissions from 25 g/m³ after adsorption to below 9.88 g /m³, achieving over 60% reduction. This approach innovatively combines the high-capacity adsorption with the precise separation of membrane technology while effectively controlling retrofit costs, offering a technically viable and economically sound solution for upgrading oil vapor recovery systems in existing oil depots.