Abstract: The effects of water on the stability of the catalyst and the product distribution were investigated through controlling the amount of water dehydrated from methanol or using HZSM5 pretreated by hydrothermal method at the analogous atmosphere of gasoline synthesis in two-stage process（360℃， 2MPa）. Physicochemical properties of the zeolite were characterized by XRD, BET, FT-IR, SEM, and NH₃-TPD. The results showed that HZSM-5 pretreated by hydrothermal method had smaller crystal size, more mesoporous, and moderate acid sites, which in all result in the enhancement of gasoline yield and the selectivity to iso-paraffins. The steam generated during methanol dehydration led to the deactivation of strong acid over HZSM-5 zeolite.