A clear understanding of the methane formation mechanism in the initial MTO process is beneficial for the illustration of the initial C–H bond activation mechanism and the first C–C bond formation route. Thus, attempts are made here to unravel the methane formation pathway in the initial MTO process by elaborately designing experiments. It is shown that methane is generated together with formaldehyde or methoxymethyl cation by attacking the C–H bond of methanol or dimethyl ether (DME) with surface methoxy species (SMS). The reaction of DME and SMS provides strong evidence for the occurrence of C–H bond cleavage and the “methoxymethyl cation mechanism” in the initial MTO process.