In order to determine the yield characteristics as well as the critical shear stress value of dewatered sludge when wall slip occurs, the rotating rheometer with parallel plate(R/S +CPS) and high-speed cameras(Trouble Shooter) are used for dewatered sludge with low moisture content, at the same time, linear marker and the sensitivity of the yield stress to shear rate as well as the dependence of the shear stress-shear rate data to parallel plate spacing are adopted, thus the existence of the slip and the critical condition can be identified. The results show that the dewatered sludge with the moisture content of 83% under the shear rate of 5~60 s -1 show that the shear thinning, and because there may be the occurrence of wall slip, the yield stress is sensitive to shear rate, and its value decreases with the increase of shear rate. For the dewatered sludge with moisture content of 84%, 85% and 86%, the occurrence of wall slip is obviously observed. Comparing with multiple sets of shear stress-shear rate data under different working conditions finds it isn’t overlap; while for the moisture content as 88%, the results is just opposite. The wall slip velocity produced increases with the increase of wall shear stress. So shear stress and moisture content have some influences on wall slip velocity, and there even may be a critical shear stress.