In this research a one-dimensional mathematical model was developed to investigate the effects of inlet temperature, pressure, and feed flow rate on an adiabatic fixed bed reactor over Na-HZSM5 catalyst for dehydration of methanol to dimethyl ether. Results indicated that temperature profile and methanol conversion are mostly affected by inlet temperature. The pressure has no significant effect on methanol conversion. Since the reaction is reversible and exothermic, increasing of inlet temperature shifts equilibrium conversion to low values. Methanol conversion predicted by this model is in good agreement with experimental data.