Abstract: Bioretention system is known to be the main technology of the management of nitrogen in urban runoff, which is effective in removing a range of pollutants, including suspended solids, heavy metals, phosphorus, oil and grease, and fecal coliform. Nitrogen removal performance, however, has been highly variable. So, a better understanding of the efficiency and process of denitrification in bioretention system is of crucial importance for the control of nonpoint source pollution in urban area. In this paper, based on data collection and analysis, advances in denitrification processes of bioretention system, including denitrification performance, influence factors and mechanism, were summarized in detail. In the end of the paper, some related advices on future research were put forward in the following aspects: To further study the processes and drivers of nitrogen removal in bioretention system; to further study the coupling response relationship among macroscopic biotope, running performance and microecosystem; and to further carry out some experiments on identifying the key characteristic of function plants with molecular biology method.