The pyrolysis behaviors of Shengli lignite (SL) pretreated with ionic liquid 1-butyl-3-methyl-imidazolium dihydrogen phosphate ([Bmim]H2PO4) was studied in this paper. The effect of pretreatment temperature and the ratio of [Bmim]H2PO4 to SL on the pyrolysis behaviors of lignite were mainly investigated. Also the mechanism of the influence of [Bmim]H2PO4 pretreatment on the pyrolysis of lignite was investigated by FTIR analysis. It is found that [Bmim]H2PO4 pretreatment results in the drastical increase of the yield of tar, especially the yield of oil fraction. The yield of tars obtained from pyrolysis of SL treated in [Bmim]H2PO4 at 200 degrees C with the ratio of [Bmim]H2PO4 to SL at 1 increases by 1.7 times compared to that of SL. [Bmim]H2PO4 pretreatment results in the increase of yield of oil fraction, especially the yield of arenes and phenolics. The FT-IR analysis shows that [Bmim]H2PO4 pretreatment results in the increase of the content of carbonyl group and ether bond in SL. (C) 2016 Published by Elsevier B.V.