In order to understand the promoting effect of char in different states on the steam reforming of biomassderived tar during the gasification process, Fallopia Japonica stem (FJS) chars were prepared at different pyrolysis temperatures with different pyrolysis time, and used as the catalyst for the reforming of tar derived from FJS itself in a fixed-bed reactor. As-prepared FJS chars were characterized using Scanning Electron Microscope (SEM), Fourier Transform Infra Red spectroscopy (FT-IR), and Brunauer-EmmetTeller ( BET) surface area measurement for clarifying the relationship between the promoting effect and the physical and chemical structures of the char. It was found that BET surface area, chemical structure, and the contents of alkaline and alkaline earth metals (AAEM) in the char, which were obviously affected by pyrolysis temperature and time, had significant effect on char reactivity as well as the catalytic activity on tar reforming. The char obtained at lower temperature (< 700 degrees C) had lower BET surface area but higher active chemical components, thus showed higher gasification reactivity but lower promoting property on tar reforming. With the increase of BET surface area, the reactivity of char itself decreased at first due to the decrease of active chemical components, and then increased to some extent due to the increase in BET surface area. On the contrary, the promoting effect of char on the tar reforming increased at first and then decreased due to the decrease of AAEM species in the char and the shrinkage of old larger pores in char which could hinder the contact between FJS-derived tar and char. (C) 2014 Elsevier Ltd. All rights reserved.