Fast pyrolysis ofglucose/cellulose Will produce abundant 1,6-anhydro-beta-n-glucopyranose (known as levoglucosam LG) as the predominant anhydrosugar product, together with certain amounts of other anhydrosugars, mainly including 1,6anhydro-,13-D-glucofuranose (AGF), 1,4:3,6-dianhydro-beta-D-glucopyranose (DGP), 1,S-anhydro-4-deoxy-p-glycero-hex-1-en-3ulose (APP); 1-h,ydroxy-3,6-dioxabicyclo[3.2.11octan-2-one (LAC). The formation mechanisms of the latter four anhydrosugar products are not well-known. at-present. Substantiated by analyticalpyrolysis gas-chromatography/mass spectrometry (Py-GC/ MS) experiments, quantum chemistry calculations are employed to give a deep insight into their formation-Mechanisms hi this study. The anomeric effect of glucopyranose has a distinct effect to their formation. DGP is mainly- derived' from glucopyranose which plays a vital role in the formation:of 1,4-acetal, ring. On the contrary, APP and LAC can merely derive from beta-D-glucopyranose drie, to the dehydration at 1-011 + 2-H site. APP is iMportant but riot necessary tO,form LAC, and their formation pathways-also compete with each Other. Moreover, AGF is not influenced by the anorneric effect-of the two anoiners, because its formation relies on: the acyclic n-glucose.