When treating waste water with low chemical oxygen demand to ammonium, the CANON process brings about a striking innovative effect. The denitrification performance of the CANON process was studied by adopting the aeration up-flow sludge bed reactor (AUSB). Under the condition of ammonia nitrogen being added as the one and only nitrogen source, the reactor shows 73% of the total nitrogen removal rate. With the gradual increase of inflow ammonia nitrogen and reduction of the hydraulic retention time, its denitrification ability continues to be promoted and the total nitrogen removal load reaches to more than 0.47 kg/(m³·d). By the 60th day since the study began, the visible particles appeared. During the start-up period, the activity of NOB in the system were suppressed effectively, and the value of Δρ(TN)/Δρ(NO₃^--N) was close to 8. After the operation of 135 d, the whole process of autotrophic denitrification of granular sludge was successfully started in a continuous flow reactor. The results demonstrated that increasing the influent load promoted the microbial growth, thus a more suitable growth conditions for CANON strain was built and NOB was gradually eliminated. By the interaction of a variety of biological populations, the reactor showed a high nitrogen removal efficiency, and the continuous flow of CANON process started successfully.