The invention provides styrene-maleic anhydride alkylphenol polyoxyethylene ether copolymer which has a structure shown as a formula I. The copolymer disclosed by the invention has better compatibility with high-colloid asphalt, can be used as a high-colloid asphaltene heavy oil viscosity reducer, has effects of dispersing asphaltene and enhancing colloid stable asphaltene, can effectively reduce heavy oil viscosity and has higher viscosity reduction rate. In an application process, the copolymer can be directly added into heavy oil, has convenience in application and low cost and further has no effect on oil quality. Embodiment results show that the styrene-maleic anhydride alkylphenol polyoxyethylene ether copolymer disclosed by the invention can be utilized as the viscosity reducer to be applied into the heavy oil; when an adding amount is 0.4% of the mass of the heavy oil, the viscosity reduction rate at 50 DEG C can reach 76% or more.