A novel demulsifier (noted as PSADP) having high molecular weight and branch structure was prepared via one-pot synthesis by using two PEO-PPO demulsifiers (SP-1 and DMEA-1), acrylic acid (AA), and pentaerythritol tetraacrylate (PET4A) as materials. The demulsification experiments showed that PSADP can achieve high water removal and clear separated water at the same time. Optimal preparation condition of PSADP was elected by orthogonal test. In addition, the study of partition coefficient and interfacial dilational moduli showed that the best PSADP had best capacity to displace the natural active agents and destroy the interface.