Abstract: Abstract: Large quantities of crop stalk resources are produced in China every year, and some of the stalks are incinerated, which pollutes the environment. Biomass gasification is attracting a great deal of attention as a way of utilizing biomass waste. In this study, a circulating fluidized bed experimental system was designed and constructed with a treating capacity of 150 kg/h, which equipped with secondary back-feeding device, steam generator and air preheater. The influences of secondary back-feeding device on the gasification performance were investigated with corn stalk after crushing and drying pretreatment as biomass feedstock. The effects of air equivalence ratio (ER) within 0.20～0.35 on gasifier temperature, tar content, gas composition, carbon conversion rate and gasification efficiency were investigated when the secondary back-feeding device was closed and open. The gasification reaction was promoted by increasing ER, and gasification efficiency and carbon conversion showed a trend of increasing firstly and then decreasing. The results showed that good gasification results were both obtained at ER of 0.26. When the secondary back-feeding device was closed, the maximum carbon conversion rate and gasification efficiency were 91.19% and 72.95%, respectively. Whereas the carbon conversion rate and gasification efficiency were higher when the secondary back-feeding device was open, which was up to 93.54% and 77.06%, respectively. The experimental results also showed that secondary back-feeding device had a good effect on tar cracking. When the secondary back-feeding device was closed and open, the tar content in gas was 7.5 g/m3 and 4.5 g/m3 at ER of 0.26, respectively, which meant that tar content can be decreased by 40% when secondary back-feeding system was open. The effects of steam/biomass ratio (S/B) on gasification characteristics were investigated when the secondary back-feeding device was open. The results showed that gas quality and gasification efficiency were improved with air as main gasifying agent and steam assisted. The better operation conditions of the corn stalk gasification were 0.26 of ER and 0.2 of S/B, and gas calorific value and gasification efficiency reached to maximum value of 5.89 MJ/m3 and 81.45%, respectively. The results of tar distillation analysis under typical operating conditions indicated that the pyrolysis conversion of tar was promoted by increasing the reaction temperature of gasifier and maintaining a certain amount of water vapor in the gasifier. The experiment can provide reference for efficient and clean transformation and utilization of straw biomass.