Abstract: Laboratory experiments were carried out by uniform design to investigate the effects of flocculant unit consumption,flocculant solution concentration and feed-slurry concentration on settling velocity and settling concentration in solid-liquid separation.According to the regression analysis of experimental data,the influence degrees of the three factors on settling velocity in descending order are feed-slurry concentration,flocculant unit consumption and flocculant solution concentration.Settling velocity shows a positive correlation with flocculant solution concentration and flocculant unit consumption,but a negative correlation with feed-slurry concentration.The influence degrees of the three factors on settling concentration in descending order are feed-slurry concentration,flocculant unit consumption and flocculant solution concentration.Settling concentration exhibits a positive correlation with flocculant solution concentration and feed-slurry concentration,but is independent of flocculant unit consumption.Nonlinear programme is used to find the optimal ratio,and the deviation of the predicted values and the measured ones from verification experiments is less than 8%.The recommended operating parameters for deep cone thickeners are the flocculant unit consumption of 5g·t^-1,the flocculant solution concentration of 0.05% and feed-slurry concentration of 5.233%.