The efficient alcoholysis of cellulose to monosaccharide is of great importance to produce fuels and fine chemicals from renewable feedstocks. In this work, the conversion of cellulose into methyl glucosides was investigated by combining the pretreatment process of the ionic liquid 1-allyl-3-methylimidazolium chloride ([Amim]Cl) and the subsequent alcoholysis catalyzed by the heteropolyacid H3PW12O40. The X-ray diffraction characterization of [Amim]Cl-pretreated cellulose shows that the pretreatment process could transform cellulose I to cellulose II resulting in the loss of crystalline structure. The subsequent alcoholysis of the pretreated cellulose catalyzed by H3PW12O40 proves to be a highly efficient way to convert cellulose to methyl glucosides in the medium of methanol. Under the optimized conditions of the [Amim]Cl pretreatment and alcoholysis reaction, the highest yield of methyl glucosides reaches up to 70.2 mass%, which is much higher than those previously published without pretreatment process.