Three bio-methods for sludge reduction including aerobic digestion, anaerobic digestion and predation by T. tubifex were investigated. The sludge reduction rates in 24h by predation of T. tubifex, anaerobic digestion and aerobic digestion were 0.13 mg x (mg x d)(-1), 0.09 mg x (mg x d)(-1) and 0.03 mg x (mg x d)(-1) respectively, when sludge concentration was 2500 mg x L(-1). T. tubifex could destroy the cell membrane of the bacteria in a short time, which could increase the sludge reduction rate when anaerobic digestion was adopted after the predation of T. tubifex. Using the T. tubifex to reduce sludge for 12h combined with anaerobic digestion for 36h could reduce sludge by 30%, and the sludge reduction rate was 0.25 mg x (mg x d)(-1). If the initial sludge concentration increased, the time of predation by T. tubifex should be extended.