Methyl methoxyacetate (MMAc), a precursor to ethylene glycol (EG), was synthesized successfully via the liquid-phase carbonylation of dimethoxymethane (DMM) catalyzed by heteropolyacids (HPAs). The experiment results showed that H3PW12O40 (PW12) exhibited the best catalytic performance for the carbonylation of DMM, and its high catalytic activity was attributed to the synergistic effect between its superior acidic strength and the high polarity of the solvent.