Abstract: To solve the problem of high concentration of suspended material and fine size particle in coal slurry in coal preparation plant,which caused difficult to treat the coal slurry,simulation studied the effect of hydraulic condition of thickening pool on coagulation result under the actual production process. The research result shows that the coagulating of high concentration coal slurry should conducted in two stages,and each stage need different hydraulic condition. In first coagulation stage,the hydraulic condition should need the requirement of forming inclusions with appropriated size and quantity. In the second coagulation stage need weak hydraulic condition to obtain big sized flock. The limit of hydraulic condition is that: when the mixing speed v₁ varied in the range of 100~150 rpm in first stage,the mixing time t₁ should controlled in 45~75 s; and when the mixing speed v₂ varied in the range of 20~50 rpm in second stage,the mixing time t₂ should controlled in 30~60 s.