Abstract: Removal and transformation behavior of chlorine in two Chinese bituminous coals (WJP and HYS coal) during sub-critical water treatment were studied in a semi-continuous apparatus. The influence of temperature and pressure on the removal of chlorine was examined; and chemical extraction was also done to determine the occurrence mode of chlorine in raw coal and its residues. The results show that the removal of chlorine in two coals all increases with increasing temperature; at 410℃, 15MPa, 60min and water flow rate of 580mL/h, the removal of chlorine is 84.6% and 72.4% for WJP and HYS coal, respectively. The maximum removal of chlorine from WJP coal, 79.8%, is obtained under 15MPa. Chlorine in HYS coal is mainly organically associated, among which 23.6% is bonded to organic cations by ion exchangeable mechanism and 76.4% is covalently-bond organic chlorine; while for WJP coal, that is 39% and 52.9%, respectively, and the other 8% is associated with inorganic matters. During sub-critical water treatment, chlorine bound to organic cations by ion exchangeable mechanism is more easily volatilized than covalently-bond organic chlorine; and the chlorine associated with organic matters will be firstly turned into inorganic form, and then released from the coal.