Abstract: HZSM-5 （HZ） zeolites were hydrothermally modified using organic bases （TPAOH, urea） and inorganic bases （NaOH, Na₂CO₃）. The modified HZ zeolites were characterized by XRD, N₂adsorption-desorption, NH₃-TPD, and SEM. Furthermore, their catalytic activity and stability in the acetalization of formaldehyde and ethanol to synthesize diethoxymethane （DEM） were investigated under various reaction conditions. Using the HZ zeolite modified with 0.10 mol/L urea solution as the catalyst, a DEM yield of 79.2% and a formaldehyde conversion of 92.2% were achieved under the conditions of an ethanol-to-formaldehyde molar ratio of 7∶1, a catalyst loading of 2.5 wt.%, a reaction temperature of 70 ℃, and a reaction time of 3 h. Modification with urea solution facilitated the formation of mesoporous structures, increased the specific surface area, and enhanced the strong acid site density of the zeolite, thereby promoting the acetalization reaction. After five catalytic cycles, the yield of DEM and the conversion of formaldehyde showed no significant changes, indicating that the hydrothermal-modified zeolite catalyst possesses excellent catalytic activity and stability.