Bioretentions represent a prevalent stormwater runoff management technique in urban areas, frequently employed to address the treatment of pollutants in runoff. However, the efficacy of nitrate-nitrogen removal by bioretention systems is subject to variation due to a multitude of environmental factors. In this study, three bioretentions (B1, B2, and B3) were constructed to investigate the migration and transformation characteristics of nitrate nitrogen in bioretentions under different soil mediums (sandy soil, sandy soil + newspaper, and sandy soil + wood chips). The findings indicated that the efficacy of nitrate nitrogen removal varied with different media types, with sandy soil augmented by wood chips demonstrating the optimal removal performance, followed by sandy soil combined with newspaper, and sandy soil alone exhibiting the least efficient removal. The B3 plant retention system demonstrated the optimal removal efficacy among the three mediums examined. The B2 medium exhibited a secondary level of effectiveness, while the B1 medium exhibited the least efficient removal capacity. With an increase in hydraulic retention time, there was a corresponding increase in the removal rate of the three bioretentions, but a concomitant decrease in the removal rate. The addition of carbon source, whether it be newspaper or wood chips, led to the swift activation of the phytoretention system, thereby enhancing the rate of nitrate nitrogen removal over a brief period.