The invention provides a polyoxyethylene-benzene sulfonate type composite dimeric surfactant and a preparation method thereof. The structural formula of the polyoxyethylene-benzene sulfonate type composite dimeric surfactant is as shown in FORMULA I, wherein n is 6, 7, 8, 9, 10, 12 or 14; m is 4, 5, 6, 7, 8, 9, 10, 15 or 20. The preparation method of the polyoxyethylene-benzene sulfonate type composite dimeric surfactant provided by the invention has the advantages that raw materials are readily available, reaction conditions are mild, and the prepared polyoxyethylene-benzene sulfonate type composite dimeric surfactant is high in purity, high in yield and favorable for enlarged production, is extremely high in surface activity, has good physical and chemical properties such as salt resistance, temperature tolerance and chemical structure stability, and can be widely applied to the field of oil exploitation.