Methanol to olefin process was investigated over a steam-treated Ca-ZSM-5 catalyst in a flow-type fixed bed reactor by adding aromatics to the methanol feed. As a comparison, the catalytic performance in the presence of nitrogen and water was also investigated. The experimental results exhibit that in the presence of aromatics, the total light olefin selectivity and the ethylene selectivity increased, while propylene selectivity increased with adding o-xylene and m-xylene to the methanol feed, but decreased with adding benzene, toluene, p-xylene and ethylbenzen to the methanol feed. The catalyst was characterized by temperature-programmed desorption of ammonia, N-2 adsorption, and scanning electron microscope. The adsorption of water and aromatics on the catalyst was also studied. Based on the results, it is concluded that aromatics may be responsible for the formation of light olefins and be more favorable for ethylene than propylene in methanol conversion.