In order to study the reaction mechanism of steam reforming of bio-oil, acetic acid was selected as the model compound and Ni/Al2O3 as the catalyst to carry out a series of experiments. Through the comparative analysis of instantaneous gases productions, composition of liquid phase products and carbon deposition, we can infer the reaction mechanism of acetic acid catalytic reforming and carbon deposition process. It is found that dehydrogenation reaction, water-gas shift reaction and methane (CHx) reforming reaction are the main source of H-2, while [CHx] catalytic cracking reaction and CO disproportionation reaction lead to carbon deposition, furthermore carbon-steam gasification reaction can consume carbon deposition to a certain extent. Acetone is an important intermediate for carbon deposition, leading to rapid deactivation of the catalyst. By characterizing the catalyst after the reforming reaction, we consider that the formation of carbon deposition mainly includes two stages: the coating of active sites and the growth of fibrous carbon deposition. The carbon deposition on the surface of used-catalyst is 0.86%, which is mainly composed of the accumulated [C=C] and [C equivalent to C] bonds. (C) 2019 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.