The invention relates to a preparation method of a titanium oxide modified microporous molecular sieve shape-selective catalyst. According to the method, a microporous molecular sieve ZSM-5 or MCM-22 is taken as a matrix, tetrabutyl titanate is taken as a precursor, absolute ethyl alcohol is taken as a solvent, titanium oxide is supported to the outer surface of the microporous molecular sieve through equivalent-volume impregnation and water-vapor treatment, and titanium oxide in the catalyst accounts for 3%-10% of the total mass of the catalyst. The shape-selective catalyst obtained with the method has good shape-selective catalysis performance on a process of synthesizing p-xylene through alkylation of toluene and dimethyl carbonate.