Abstract: The catalysis mechanism of potassium salt in rapid pyrolysis of cellulose was studied in an infrared radiation bench scale reactor. The results show that potassium salt restrains the formation of aqueous oil, while enhances the formation of char and gas. On the basis of the distribution diagram of metallic salt by electron microscopy, and the content determination of metallic ion in aqueous oil and char, catalysis of potassium salt mainly occurs in solid phase during cellulose pyrolysis. It selectively catalyzes some reactions in the form of ion, and accelerates the cracking and splitting process of molecules. It causes a reduction of levoglucosan formation, and improves the production of hydroxyacetaldehyde, acetaldehyde and small molecule components including methanol, ketone or aldehyde.