The invention discloses a method for synthesizing an alkylphenol-polyethenoxy ether terpolymer surfactant, relating to ether surfactants used as a solubilizing agent, a wetting agent, an emulsifier and a foaming agent; the surfactant prepared with the method has a structural formula as follows, wherein EO is ethyleneoxide group (-CH2CH2O-), the addition mole number m thereof can be 4, 7, 10, 15, 20 or 30, and n can be 8, 9, 10 or 14; the synthesizing method comprises the following steps: firstly, 2-(3-(5-alkyl salicyl)-5-alkyl salicyl)-4-alkyl phenol is synthesized and an ionic liquid catalyst is added into the reaction of 4-alkyl phenol and paraformaldehyde; and secondly, the product of alkylphenol-polyethenoxy ether terpolymer surfactant is synthesized. The method has simple technique, adopts the recyclable ionic liquid catalyst, effectively reduces the environmental pollution and has short reaction time and higher yield of product.