Abstract: A new control strategy of both hardness and concentration of coal slurry is proposed.Hardness and concentration are feed forward disturbance variables,while overflow concentration is feedback control variable,they formed feed forward-feedback control system.Based strategy above mentioned,an automatic control system designed for reagent addition for coal slurry settling,by which the overflow concentration of thickener can be managed below 8g/L,and closed recirculation for water is effected.