Abstract: Effects of cationic surfactant (CTAC) and cationic polyacrylamide (CPAM) on sludge dehydration ability were studied by testing the moisture content and extracellular polymeric substance (EPS) of sludge. Experimental results indicate that the dehydration ability of sludge treated with CTAC or CPAM is improved. The optimum dosages of CPAM and CTAC are 0.0106 gram to 100 ml sludge and 0.738 gram to 100 ml sludge respectively, which make the moisture content of filtered sludge down to 80.28% and 68.73% respectively. In order to explore the action mechanism of CTAC on sludge, scanning electronic microscope (SEM) and size distribution were made to the sludge before and after treated with CTAC. It is found that the sludge's origianl floc structure is destroyed after treatment of CTAC, then the surface of sludge is in a web structure, and the sludge's granule size which accounts for 90% of the volume fraction is below 52m, obviouly lower than that in the original sludge. It concludes that CTAC improves sludge's dehydration ability through destroying its structure, thus makes the sluge release gap water and EPS.