Abstract: The activity and stability of hydrolysis of dimethyl ether over HZSM-5 molecular sieve at different temperatures under a space velocity as high as 18000 mL/gcat·h were investigated. The effect of Si/Al ratio on the properties of HZSM-5 during hydrolysis was studied. The results showed that HZSM-5 exhibited high activity for the hydrolysis of dimethyl ether but easily lost its activity due to coke formation at low Si/Al ratios or at high temperatures. For the process of steam reforming of dimethyl ether，a composite catalyst consisting of HZSM-5-50 (Si/Al ratio is 50) and self-synthesized Cu-Zn-Al (mole ratio is 3∶5∶2) catalyst was prepared simply by mechanical mixing. The dimethyl ether conversion and H₂ selectivity over the composite catalysts with different weight ratios of two components were measured. In addition，the influence of space velocity of feed gas on the process was examined as well. The results showed that the composite catalyst (the weight ratio of Cu-Zn-Al to HZSM-5-50 1∶1) could maintain its catalytic properties for a relatively long time during the reaction at 275 °C and space velocity of 18 000 mL/gcat·h. The maximum H₂ yield around 54% could be obtained while the space velocity was controlled at an appropriate level，near 4000 mL/gcat·h.