Abstract: The removal of mercury from coal using sub-critical water extraction in a semi-continuous reactor was studied. The effect of temperature, pressure and extraction time on the removal rate of mercury was examined. The results show that in the temperature range 290 ℃～380 ℃, the higher the temperature is, the larger the mercury removal rate is. And the mercury removal rate increases with reaction pressure and residence time under the pressures from 5 MPa to 15 MPa and residence time from 10 min to 100 min. The maximum removal rate of mercury can reach above 96% under the conditions of 380 ℃, 15 MPa and 60 min.