Herein, we report the effect of the hot-water pretreatment on the catalytic activity of the H-mordenite (H-MOR) zeolite for DME carbonylation. The structure and acidity of the H-MOR catalysts pretreated by hot water were systematically characterized by XRD, nitrogen adsorption, SEM, H2O-TPD, NH3-TPD, H-1 NMR and NH3-DRIFTS technologies. With the increase of the duration of the hot-water pretreatment, the catalytic activity shows a volcano-type variation. The H-MOR catalyst pretreated by hot water for 10 min at 573 K displays the highest catalytic activity among all of the catalysts. The appropriate duration of the hot-water pretreatment can generate new medium strong and strong Bronsted acid sites, which changes the microenvironment in the pores of H-MOR. Additionally, the newly generated Bronsted acid sites will accelerate the first step of DME carbonylation, that is, DME reacts with the Bronsted acid sites of the zeolite forming surface methoxy groups and methanol, improving the catalytic activity of the catalysts. However, too long duration of the hot-water pretreatment will remain water molecules in H-MOR, which inhibits DME carbonylation.