In this study, the changes on physicochemical characteristics of pretreated and digested smooth cordgrass were investigated by the composition, X-ray, FTIR and C-13 NMR, and TG analyses. Simultaneous lime treatment and dry digestion could be successfully carried out in leaching bed reactor at thermophilic condition with highest breakage of lignocellulose and higher biogas yield. Comparing with mesophilic condition, thermophilic condition brought a greater change of lignocellulosic structure, thus making holocellulose more accessible to anaerobic bacteria and benefiting to biogas production. The removal of lignin and hemicellulose at pretreatment phase was shown by the cleavage of ester linkage or carbonyl groups and the reducing intensity of lignin from FTIR and C-13 NMR spectra analysis. The removal of polysaccharide mainly happened at digestion phase, as shown by the results of composition, FTIR and C-13 NMR analysis. The crystalline index obviously decreased at pretreatment and digestion phases, as indicated by the intensity change of hydrogen bonding. The results of TG analysis showed that pretreatment and digestion had an obvious impact on the distribution of volatile matter, rate of weight loss and kinetic parameters of pyrolysis. (C) 2011 Elsevier B.V. All rights reserved.