The invention relates to a composite mesoporous molecular sieve solid superacid and a preparation method thereof. According to the method, a home-made mesoporous molecular sieve is used as a carrier, a sol-gel method and an impregnation method are adopted to dope TiO2 and load SO4<2-> to obtain the novel molecular sieve loaded oxide solid superacid SO4<2->/TiO2/MAS-5 which is used as a catalyst to prepare propylene glycol monomethyl ether acetate (PMA) by taking propylene glycol monomethyl ether (PM) and acetic acid (HAc) as materials for esterification reaction so as to achieve probe reaction, thus optimizing the formula and loading conditions of TiO2 and SO4<2->. Compared with existing SO4<2->/TiO2 solid superacid catalysts, the catalyst disclosed by the invention has the advantages of high acid strength, high catalytic activity, large specific surface area, long service life and good stability, and has wide industrial application prospect.