The invention discloses a method for catalyzing an alpha-pinene dimerization reaction through a Bronsted-Lewis acidic inorganic-organic composite polyoxometalate catalyst Mn<0.5>[MIMPS]<2>PW<12>O<40>. The method is characterized by introducing a proper Bronsted acid center and metal Lewis acid center into an ionic-liquid-like cation structure of the catalyst in form of covalent bonds and ionic bonds, respectively. The catalyst is simple in preparation method and clear in structure and keeps active components stable and free of running off. The catalyst shows excellent catalytic activity and stability in an alpha-pinene dimerization reaction. The method is simple and convenient to operate, and the catalyst is easy to separate and reuse and is eco-friendly. The method develops a new feasible approach for high-value-added deep processing of alpha-pinene to replace fossil resources.