Potassium is a well-known alkali catalyst in the thermal reactions of biomass. The effect of potassium on the pyrolysis behavior and kinetics of biomass was investigated through TGA and a fixed bed in this study. The addition of potassium reduced initial and peak temperature in TGA curves, promoting the decomposition process of biomass. The effect of potassium on the apparent activation energy varies at different conversion degree (a) and lower apparent activation energy was obtained at the initial stage (a <= 0.3) of the pyrolysis process. The influence of potassium on the volatiles releasing behavior was dependent on the amount of loading potassium. The gas yield was significantly increased with the increasing of potassium concentration when the impregnated potassium was below 0.3 mol/kg. Particularly, the yield of H2 and CO2 was promoted by potassium. Higher potassium content may contribute to the increase in reactivity towards tar molecules, leading to quickly decrease in tar yield. The surface chemical characteristics of char were determined by FTIR spectroscopic method. Above a certain threshold surface concentration of potassium, SEM analysis shows that agglomeration is a potential threat at high temperature, which can block the active sites and decrease the activity during biomass thermal decomposition. (C) 2016 Elsevier Ltd. All rights reserved.