A derivation method based on bezoylation was applied to quantitative analysis of three typical anhydro-sugars obtained from pyrolysis of cellulose on a fixed bed reactor. The experimental results showed that this precolumn HPLC derivatization was proved to be an efficient and accurate method for the rapid determination of anhydro-sugars. Cellobiosan and cellotriosan may be produced via thermal cleavage of glycosidic bonds during cellulose pyrolysis rather than secondary polymerization of the levoglucosan. The higher DPs anhydro-sugars had less thermal stability and they were more susceptible to decomposition at the higher temperature.