The invention discloses a nanometre complex solid superacid which is a composite S2O8<2->/ZnFe2O4 composed of S2O8<2-> and ZnFe2O4. The nanometre complex solid superacid is in spinel structure, the average grain diameter of crystal grain is 20-60nm, acid strength is -11.99--14.52, specific surface area is 120-190m<2>/g, and the mass percentage of sulphur is 1.8-6.5%. The catalyst is prepared by using a coprecipitation-immersion method with simple preparation route and low cost, and the obtained catalyst has the advantages of complete crystal form, small crystal particle diameter, big specificsurface area, high catalytic activity, long service life and the like. When used for catalyzing and synthesizing benzyl acetate, the nanometre complex solid superacid S2O8<2->/ZnFe2O4 of the invention has the esterification rate of 98.0%, and has the advantages of simple and easily-controlled operation, no three-waste pollution, good product quality and low production cost.