Abstract: The lignin from rice straw was separated at the temperature of 160 ℃ by the modified method of high boiling solvent (HBS). In the process, the composite catalyst of sulfuric acid and acetic acid was used and the auxiliary agent G was added. The obtained optimum technological conditions were as follows: 55 g desiccated rice straw, liquid solid ratio 6∶1, mass ratio of the auxiliary agent G to 1,4butanediol 1∶10, the dosage of sulfuric acid in the composite catalyst 4 g, heat preservation at 160 ℃ for 1 h. The yield of lignin is 16.02 %. The process advantages are relatively low temperature and less dosage of solvent.