The current paper concerns the process of non-woody biomass gasification, particularly about releasing processes of detrimental elements. The gasification of corn straw was carried out in a downdraft fixed bed gasifier under atmospheric pressure, using air as an oxidizer. The effects of the operating conditions on gasification performance in terms of the temperature profiles of the gasifier, the composition distribution of the producer gas and the release of sulphur and chlorine compounds during gasification of corn straw were investigated. Besides, the gasification characteristics were evaluated in terms of low heating value (LHV), gas yield, gasification efficiency and tar concentration in the raw gas. According to the experimental results, operating conditions have great influence on the temperature profiles of the gasifier and the composition distribution of the product gas. During the gasification of non-woody biomass, the variations of the concentration of sulphur and chlorine compounds in gaseous and ash are not a monotonic tread under different operating conditions. Besides, over the ranges of the equivalence ratio(ER) examined, higher or lower ER both degraded the quality of gas and gasification efficiency. If ER is regarded as a function of the combustible species, the optimum value of ER is 0.28-0.32, and the optimal LHV of 5.39 MJ/Nm(3), gas yield of 2.86 Nm(3)/kg, gasification efficiency of 73.61% and tar concentration of 4617 mg/Nm(3) is obtained at different ER. Copyright (C) 2011, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.