The effects of pre-swelling treatment of Shenhua coal at mild temperatures (less than 160 degrees C) on its hydro-liquefaction properties were determined in this paper. It was found that with the increase of pre-swelling temperature in tetralin (THN) up to 120 degrees C, the liquefaction conversions of swollen coals increased. However, when N-methyl-2-pyrrolidinone (NMP) was used as swelling solvent. the liquefaction conversion decreased with the increase of pre-swelling temperature. The liquefied product distributions were very much dependent on the pre-swelling pretreatment conditions, and the mechanism was discussed. Based on the results obtained, a new swelling-liquefaction combining technology (SLCT) was advanced, in which the liquefaction conversion and oil + gas yield were enhanced. (c) 2009 Published by Elsevier B.V.