A set of experiments on biomass/coal co-combustion were performed to investigate the ashing behavior in a tube furnace and a Muffle furnace respectively. The eight blending samples in terms of coal contents were 0, 5, 15, 20, 40, 60, 90, and 100 wt.%. The blending ratios of coal/straw caused different ash quantity effects, ash quantity was inhibited when the coal ratio was from 5 wt.% to 15 wt.%, and promoted when higher coal ratios. Combined the morphology analysis, mineral analysis, and chlorine equilibrium analysis, the chlorine content in the drop-tube furnace ash rapidly decreased when the coal ratio was from 5 wt.% to 15 wt.%, and the Cl content of the fly ash from 40 wt.% coal blend was very low at 0.49%. In the ash from the 40 wt.% coal blend, the CaCO3 and CaSO4 contents were very low for coupling reaction between the biomass and coal minerals under high temperature, the new and stable CaAl2Si2O8, K2Fe4-Si12O30, and KAlSi3O8 minerals were produced, which accompanied the ash promotion effect. The ashing behavior of 40 wt.% coal-blending is largely significant in preventing slagging and corrosion during straw co-firing and coal plant operation. (C) 2013 Elsevier Ltd. All rights reserved.