To develop a green synthesis route for cashew phenol-based polyether ester demulsifiers, replacing the traditional ethylene oxide and propylene oxide routes. Biomass cashew phenol and formaldehyde were used as raw materials to prepare cashew phenol aldehyde resin initiators via condensation reaction. Then, ring-opening polymerization with ethylene carbonate was conducted under the catalysis of potassium carbonate. The chemical structure of the target product was confirmed by infrared spectroscopy and 1H NMR. The demulsification performance evaluation showed that under the conditions of a demulsifier dosage of 200 mg/L, 70 ℃, and 2 h, the dehydration rate reached up to 92.25%. This study provides a new idea for the development of environmentally friendly and efficient crude oil demulsifiers, and expands the application of cashew phenol in the field of high value-added fine chemicals.