Abstract: Experiments were performed to study the effects of water content, filamentous bacterium, anaerobic time and pH, etc. on the sludge dewatering ability, and to determine the proper mechanic dewatering conditions. The results showed that optimum water content for condensing sludge to be dewatered by mechanical means is 97%. At this condition, the lowest SRF of adjusted sludge and the highest utilized rate of flocculants were obtained with the ratio of flocculant dosage to dry sludge amount of less than 0.3%; the amount and length of filamentous bacterium have an effect on the water form in sludge and change sludge dewater ability; at anaerobic condition, deoxidize sugar content is correlated with dewatering ability; the SRF decreased when pH was adjusted to near to sludge PI.