Based on the products distribution from fast pyrolysis of cellulose and levoglucosan（LG），it was determined that competing pyrolytic pathways were responsible for the formation of LG，other anhydrosugars，furans，light linear carbonyls and other products during the fast pyrolysis process.According to the catalytic effects of the four metal chlorides，the pyrolytic pathways for the formation of LGO，LAC，DGP，HMF and FF from depolymerization and dehydration of cellulose，as well as the formation of HAA and acetol from pyrolytic ring scission were discussed.Furthermore，experiments on secondary catalytic cracking of primary products were performed.The results indicated that LGO，LAC and DGP could be produced through the impregnation of FeCl3 or ZnCl2，but these anhydrosugars were sensitive to the catalysts.HMF， HAA and acetol could be produced through the impregnation of KCl.FF could be produced through the impregnation of ZnCl2，while moderate secondary cracking by ZnCl2 would promote the yield and purity of FF.