In consideration of the easy blockage of the existing thickener underflow drainage, the provision of a largescale thickener to dredge at any time the blocked pipeline arising from the pulp sedimentation can greatly reduce the potential pipeline blockage. The practical application shows that this thickener can dredge at any time the blocked pipeline arising from pulp sedimentation to effectively, avoid the pulp deposition in the pipeline, greatly reduce the possibility of the pipeline blockage with good effect, which is worth to be popularized.