The current study aimed to investigate catalytic behaviors of alkali metal salt participating in homogeneous steam-volatile and heterogeneous steam-char reforming reactions in steam gasification of cellulose. The results indicate that the temperature is a key parameter which significantly influenced both yield and composition of gas and tar and catalytic performances of KCl. Externally added steam had negligible effect on cracking/reforming of macromolecules volatiles at the temperature of 700 and 900 degrees C without KCl, whereas in the presence of KCl, it would be activated and further reacted with low reactivity macromolecules volatiles, leading to an increase in gas yield and a decrease in tar yield. KCl was notably involved in homogeneous steam-volatile reactions, and enhanced the water gas shift reaction and tar reforming reactions. However, KCl had little promotion effect on thermal cracking/reforming of levoglucosan in homogeneous steam-volatile reforming process at 500 degrees C. Its inhibition effect on levoglucosan formation mainly acted during the primary pyrolysis reactions. KCl could also enhance heterogeneous in situ char-steam reaction resulting in a higher H-2 yield. The general pathway of KCl involved in homogeneous/heterogeneous reactions in steam gasification of biomass was eventually proposed.