n the northwest of China, poplar is the main species that reproduces trees used for commercial plantation, shelter forests against wind and fixing sand, agricultural protection forest and landscape engineering. The amount of poplar processing residues can be up to 10–15% of the wood volume. Therefore, large amount of poplar processing residues yielded from the wood process, such as wood cuttings, sawdust and sapwood are usually burned or dis- carded which causes environmental pollution (Jian, 2006). Using poplar processing residues as substrate of anaerobic digestion for bioenergy production will be a viable option, not only for reducing the pollution, but also for producing renewable energy.