Abstract: In order to reveal the microbial community distribution of ammonium oxidizing bacteria and the removal mechanism of NH4-N in constructed rapid infiltrition system (CRI), sands of different depths were sampled from CRI in Shenzhen, and were analyzed by denaturing gradient gel electrophoresis (DGGE). The profiles of DGGE show that the microbial community of ammonium oxidizing bacteria increases followed by a decrease from top to bottom. There are about 4~5 species in the upper 10 cm part, and they are composed of microorganisms in sewage or those who played important roles in the biodegradation of organonitrogen. About 9 species are found in CRI between 20 cm and 90 cm in depth, where the nitrosation capacity is stronger. For lack of NH4-N or oxygen, the species of ammonium oxidizing bacteria reduce to 5~6 at the depth below 100 cm. The results will be that, the upper level the ammonium oxidizing bacteria distribute in CRI, the higher the removal rate of NH4-N. The relationship between community distribution of ammonium oxidizing bacteria and the removal rate of NH4-N is meaningful to improve the treatment performance of CRI.