The invention discloses a visible light-responsive composite oxide photochemical catalyst Ba1-xSrxLi2Ti6O14 and a preparation method thereof. The chemical composition general formula of the composite oxide is Ba1-xSrxLi2Ti6O14, wherein x is more than or equal to 0 and less than or equal to 1. The preparation method comprises the following steps: weighing and burdening 99.9% analytically pure chemical raw materials, namely Li2CO3, TiO2, BaCO3 and SrCO3 according to the chemical formula Ba1-xSrxLi2Ti6O14, wherein x is more than or equal to 0 and less than or equal to 1; mixing the burdened raw materials and placing the mixed raw materials into a ball milling tank, adding zirconium oxide balls and absolute ethyl alcohol, carrying out ball-milling for 12 hours, mixing while levigating, takingout the mixture, drying and sieving by virtue of a 200-mesh sieve; and presintering uniformly mixed powder at the temperature of 900-1050 DEG C, insulating for 8-10 hours, naturally cooling to room temperature, and then reducing the particle diameter by adopting a smashing means such as a ball milling machine until the particle diameter is less than 2mu m, thus the composite oxide photochemical catalyst Ba1-xSrxLi2Ti6O14 powder is obtained. The preparation method disclosed by the invention is simple and has low cost, and the prepared photochemical catalyst has the advantages of good catalyticproperty, function of decomposing harmful chemical substances under the irradiation of visible light and good stability.