The invention discloses a compound demulsifying agent capable of improving the demulsifying effect of polyether demulsifying agents. The compound demulsifying agent is prepared through the method which includes the following steps that firstly, polyether demulsifying agents with different initiators are prepared, the initiators and a basic catalyst are added into a reactor with a stirring and condensing device, heating is carried out, epoxypropane is introduced, the mixture is fully reacted with the temperature controlled to be 115-145 DEG C and the pressure controlled to be 0.4 MPa, vacuum pumping is carried out for 30 min, ethylene oxide is introduced under the same condition, and after the mixture is fully reacted, the polyether demulsifying agents are obtained, wherein with the raw materials of the initiators, epoxypropane and ethylene oxide 100% by weight, the initiators account for 0.4-6% of the total weight, epoxypropane accounts for 30-65.6% of the total weight, ethylene oxide accounts for 20-50% of the total weight, and the dosage of the basic catalyst accounts for 0.1-5% of the total weight; secondly, the prepared polyether demulsifying agents and a flocculating agent are dissolved with a solvent and then stirred evenly, and the compound demulsifying agent is obtained, wherein the polyether demulsifying agents account for 40-70%. The obtained flocculating agent-demulsifying agent has the advantages of being small in dosage, high in dewatering rate, ideal in dewatering effect and the like.