Abstract: Low pressure steam explosion technology was utilized for pretreating the lignin in wheat straw in this paper. Single factors such as operating pressure, liquid to wheat straw ratio, granularity and reaction time were studied during the process of steam explosion for impacting their effect on conversion of lignocellulose, the maximum of lignin degradation ratio attained 22.67%. The integrated effect of the above factors on lignin degradation was investigated through L9(34) orthogonal test and the results were operating pressure superior to liquid to wheat straw ratio, liquid to wheat straw ratio superior to reaction time and reaction time superior to granularity, the optimum condition was operating pressure 0.6MPa, liquid to wheat straw ratio 20︰1, reaction time 30min and granularity 20~60 mesh respectively, the optimized result was validated further. The predominant peaks of lignin decrease through FT-IR Spectroscopy analysis, which indicates that the structure of lignin was destroyed. Morphological analysis shows that fasciculi of wheat straw was broken and the wheat straw structure got porous.