The raw water property changes greatly during the whole year leading to different sludge components and sludge characters in different periods. The Results of experiment on thickening property of sludge in water treatment plants of zhong-yin indicate that solid content of water waste is much higher, the sludge sedimentation velocity is much slower, the compression point is more indistinct. When the solid concentration is up to the critical concentration, in order to enhance sedimentation property, need to adjust the sludge charge cycle of sedimentation tank and filter runs timely; the sludge sedimentation property is similar when the sludge component is diverse during both the usual period of raw water and the low temperature and low turbidity period, the critical concentration is 0.20%; on the other hand, the sludge sedimentation property of the low temperature and high turbidity period is different to another two periods, and the critical concentration is 0.95%.