The degradation kinetics of ammonia nitrogen and COD and the microbial communities in an intermittent-flow shortcut nitrification reactor were investigated to remove ammonia and organic matters from landfill leachate. The results show that when pH=6.5-8.5, the degradation of ammonia conforms to the Michaelis-Menten model while the COD degradation is suitable for Aiba kinetic model. With the increase of pH, the maximum degradation rate and saturation constants of ammonia and COD increase first and then decrease, reaching the maximum values when pH=7.5. The results indicate that the degradations of ammonia and COD are influenced by pH, and the optimum pH should be controlled between 7.5 and 8.0. In addition, the degradation rate and the maximum degradation rate of COD are 5.6-11.3 and 12.4-16.8 times higher than those of ammonia in the shortcut nitrification process, respectively. This may be because that the high concentration of organic matters in influent leads to the heterotrophic bacteria to grow faster than autotrophic bacteria in the biological system. Finally, the domain species of ammonia oxidizing bacteria (AOB) in the reactor are Nitrosomonas europaea ATCC19178, Nitrosomonas stercoris and Nitrosospira sp.PM2, accounted for 66% together, indicating that the AOB was the predominant species for ammonia removal in this intermittent-flow shortcut nitrification reactor.