Abstract: HZSM-5 molecular sieves modified with single-component such as P、 B、Cu、Mg and multi-component such as Mg/Si, Mg/P and Mg/P/Si were prepared by impregnation, and characterized by means of XRD, BET and NH3-TPD. Selective alkylation of toluene with methanol was investigated in a fixed-bed down-flow reactor. Moreover, the microstructure and surface acidity of modified HZSM-5 were correlated with the selectivity of para-xylene. The results showed that the HZSM-5 modified with monocomponent 20%MgO has high selectivity of para-xylene (>60%) due to the decrease of pore size and quantity of strong acid sites located in the surface of catalysts after modification; and the HZSM-5 modified with multicomponent such as Mg/P/Si has no obvious effects on the promotion of p-xylene selectivity due to the interreaction of different modifier.