A pre-concentrator-GC-MS/FID was used to investigate the characteristics of volatile organic compounds (VOCs) based on the flue gases emitted from five biomass-pellets-fired boilers in this study. And the concentrations of particle matter, nitrogen oxides (NO), sulfur dioxides (SO2) and mercury and its compounds were also measured. Results demonstrated that the concentrations of SO2 and mercury and its compounds emitted from all five boilers were relatively low, which were lower than the national emission standard, while NO and particles from some boilers were higher than the standard. The mass concentration of 56 VOC species was in the range of (872.43±293.80)-(6929.66±1137.25) μg·m-3, and the analysis of influencing factors implied that the furnace temperatures and loads havd strong negative correlations with the concentration of total VOCs. The emission components of VOCs were mainly composed of alkenes (41%-59%) including ethylene, 1-butene, cis-2-butene and 1-hexene; alkanes (27%-49%) including hexane, isopentane and cyclopentane; and aromatics (6%-18%) including benzene and toluene. Moreover, the maximum incremental reactivity (MIR) method was applied to analyze ozone formation potential (OFP) of VOCs. The contribution of OFP of five boilers was mainly from alkenes, occupying a relatively high percentage of 76%-90%, and that of alkanes was in the range of 6% to 19%.