The reasons for the pressure rake of deep cone thickeners were studied On the basis of deep cone model dynamic settlement test and rheological parameters measurement. It is found that there are two reasons leading to the pressure rake of deep cone thickeners. The first is poor flocculation sedimentation caused by the fluctuations of incoming tailing concentration and flocculant dosage; and the second is the slurry's rheological parameters mutation resulting from the difference of deep cone slurry concentration distribution caused by intermittent filling discharge. This research on the pressure rake of deep cone thickeners can provide a theoretic basis for deep cone normal operation, accident forecasting and getting rid of accidents.