From the experimental results of methanol conversion over HZSM-5 catalyst, it was observed that around 250℃ methanol was only dehydrated to DME（dimethylether） and the aromatization was promoted by the autocatalytic reaction of light olefins around 310℃. When water was added to the reaction mixture, the selectivities to light olefins and aromatics were found to increase and the degree of deactivation to decrease due to the ateam distillative effect exerted by water present in the pore. In case of HZSM-5 catalysts modified by metal impregnation, it was noticed that the Br nsted acid sites decreased because of the partial ion-exchange of H⁺ ions by metal ions and that redistribution of acid sites occurred since metal ions and metal-oxides gave rise to an increase in the Lewis acid sites. Also, it is evident that the crystalline metal oxide formed on the catalyst surface during the course of calcination played the role of pore-plugging. For these reasons, the metal impregnated HZSM-5 catalysts showed lower activity and lower rate of deactivation in comparison to the HZSM-5. In particular, the modified catalysts gave substantially higher selectivities to light olefins at the level of 100% conversion of methanol.