Abstract：An upflow anaerobic sludge bed （UASB） was established to study nitrogen removal performance， microbial community and sludge characteristics in wastewater treatment by anammox under different influent concentrations. Results showed that the removal rates of ammonia nitrogen and total nitrogen were 99.33% and 92.96%， respectively， for high-strength wastewater. When influent N-concentration was low， the removal rates of ammonia nitrogen and total nitrogen were 91.99% and 74.09%， respectively. Scanning electron microscope （SEM） results showed that the sludge in the reactor gradually changed from the dominant short rod-shaped microorganisms to spherical-shaped ones. Results of microbial community structure analysis showed that Proteobacteria was abundant at the population of 29.68%. Two kinds of anammox bacteria， Candida Brocadia and Candida Jettenia， were found in the reactor. under high N-concentration condition， the abundance of Candida Jettenia was at 1.24%. while the abundance of Candida Brocadia reached at 1.23%， which replaced Candida Jettenia as the dominant genus， for low strength wastewater.