The DFT investigation of methanol and dimethyl ether (DME) carbonylation at different sites of FER zeolite is carried out in an attempt to explore whether some specific acid sites are present to selectively catalyze the desired reaction. It is shown that the surface methoxy groups (SMG), generated by the reaction of methanol or DME with the Bronsted acid sites of zeolites, preferentially forms in the 8-membered ring (8MR) and 10-membered ring (10MR) channels. Further study of the CO attack on the SMG shows that, the carbonylation reaction occurs selectively at the 6MR zone of 8MR channel of FER zeolites. This result not only provides a theoretical perspective for the experimentally observed higher carbonylation reactivity of SMG located inside the 8MR channels, but also makes the location of the reaction more accurate.