Experimental research on cellulose pyrolysis under catalysis of metallic salts was done on a thermobalance and a rapid pyrolysis system. Thermogravimetric analysis showed that K+ catalyzed the formation of active cellulose strongly and decreased the activation energy of cellulose pyrolysis. Experimental results indicated that K+ would promote the formation of char and restrain the production of bio-oil largely. Fe2+ had a similar catalysis effect on cellulose pyrolysis with K+. Fe2+ particularly catalyzed the formation of small molecule gaseous product while K+ the formation of char. The addition of K+ or Fe2+ resulted in a reduction of levoglucosan formation, and enhanced the production of hydroxyacetaldehyde and other small molecule components. Levoglucosan and hydroxyacetaldehyde were formed by the decomposition of active cellulose in a parallel mode. The secondary cracking of levoglucosan would also produce hydroxyacetaldehyde. A modified cellulose pyrolysis mechanism model was proposed based on the B-S model.