Abstract: Hybrid poplar was preprocessed with benzene-alcohol at 50 ℃, and then hybrid poplar residues were preprocessed with alcohol-alkali solution. The effects of alkaline concentration, temperature and time on the yield during the extraction of hemicellulose from hybrid poplar residues were investigated using orthogonal design method. The results showed that NaOH concentration had the most significant impact and extraction time had the least impact. The optimal extraction conditions were: NaOH concentration 8 %, reaction temperature 90 ℃ and extraction time 12 h. The hemicellulose yield was 87.20 % under the conditions. The obtained hemicellulose was characterized using the Fourier Transform Infrared Spectrometry, Nuclear Magnetic Resonance Spectrum and component analysis. The results showed that the hybrid poplar hemicellulose consisted of 4-O-methyl-D-glucurono-D-xylan with the mole ratios of Xyl∶GA of 22.83∶1 and glucosyl mannan with the mole ratios of Man∶Glu of 3.46∶1, and their contents were about 86 % and 4 % of all hemicellulose carbohydrate, respectively. Other hemicellulose fractions were a bit lower. It also contained about 4.5 % of lignin components.