Abstract: The delignification of wheat straw by alkali-oxygen-anthraquinone cooking was studied.The results showed that when temperature was 140℃,anthraquinone was 0.6%, the concentration of NaOH was 6%,the pressure of oxygen was 0.8 MPa,the ratio of solid(wheat straw) to liquid was 0.13, the rate of delignification and lignin in cellulose were 88% and 2.2%, respectively.The structures of lignin analyzed by means of IR and GC-MS spectrum indicated that there were syringyl and guaiacyl in lignin and the macro-molecules of lignin were changed into micro-molecules of lignin after cooking.