Abstract: Pre-combustion desulfurization of coal is an important method to control SO2 emission in a coal fired power plant. Desulfurization of Huayinshan coal with sub-critical water in a semi-continuous reactor was studied. The effects of temperature (320℃~450℃), pressure (5MPa~15MPa) and extraction time (10min~100min) on the removal of sulfur and weight loss of coal were examined. The results show that with the increase of temperature, pressure and reaction time the weight loss of coal and the removal of total sulfur in coal increase, and with the increase of temperature and reaction time the removal of organic sulfur-increases. At higher temperature, sub-critical water has the characteristic of selective desulfurization. The inorganic sulfur removal is mainly a physical process. Below 370℃ the organic sulfur removal is higher than inorganic sulfur removal, but above 370℃ it is opposite. It is suggested that considering the practicability, the suitable high temperature and low pressure should be taken in the sub-critical water operation condition.