The invention relates to a preparation method of a solid superacid catalyst. The preparation method of the titanium dioxide persulfate-loaded mordenite solid superacid catalyst, which is characterized by comprising the following steps: 1) preparing activated natural mordenite; 2) preparing titanium dioxide sol; 3) adding the activated natural mordenite into the titanium dioxide sol, stirring for 40-80 min, forming uniform gel, aging for 12-24h, and obtaining the gel after aging; and 4) mixing the gel after aging with ammonium persulfate, obtaining mixture, transferring the mixture into a polytetrafluoro-lined stainless steel pressure-resistant reaction tank, leading the temperature to be constant for 2-6h at 110 DEG C, filtering a product, washing with water at 60 DEG C, drying, calcining at the temperature of 400-600 DEG C for 4h, and obtaining the titanium dioxide persulfate-loaded mordenite solid superacid catalyst. The titanium dioxide persulfate-loaded mordenite solid superacid catalyst is characterized by high activity, good stability and high-efficient catalysis of dehydration reaction of fructose-rich biomass.