Display omitted Toluene as a model tar compound was used to study the effect of atmosphere on carbon deposition during biomass tar reforming. A novel Ni-loaded on lignite char (Ni/LC) and commercial Ni/Al2O3 was employed for stability evaluation in a thermogravimetric analyzer. The mechanism of coke formation under N2, H2 and steam with different steam/carbon (S/C) ratio were investigated during 5 h test. Nickel particle growth is the main reasons responsible for the deactivation of Ni-based catalysts for tar reforming. Steam remarkably suppressed the carbon deposition on Ni/Al2O3, especially in a high S/C ratio. Ni/Al2O3 exhibited high activity and stability for 5 h operation in S/C ratio of 2. H2 significantly promoted the carbon deposition on Ni/Al2O3 and caused the catalyst deactivation within 0.5 h. Ni/LC exhibited great resistance to coke deposition under inert and H2 reforming of toluene. The catalysts before and after catalytic cracking were characterized by X-ray diffraction and transmission electron microscopy to investigate the behavior of carbon deposition. Except for H2 reforming, an obvious change of the Ni crystallite size (NCS) can be found after reforming for 5 h under all conditions used in this study. The NCS in Ni/LC was significantly increased with increasing time and S/C ratio, which should be partly responsible for the deactivation of the Ni/LC.