Microsensors were applied to study the diffusion reaction and activity of a nitrogen species of deposit sediment from a drinking water supply system. Microprofiles of dissolved oxygen (DO), NH-N, NO-N, and NON in the sediment indicated that the DO concentration decreased from the highest at the sediment surface to zero at the bottom of the sediment. Similarly, with the increase of depth, NH-N initially increased rapidly and then decreased slowly, while the concentration of NO-N reached a maximum at around 6000 μm and then decreased to about 0.1 mg·L near the bottom of the sediment. Almost no change was observed for NO-N. The decrease of NH-N and DO corresponded well with the increase of NO-N. Furthermore, based on a consumption and production rate analysis, DO has always been consumed; the NH-N consumption rate increased rapidly within 0-1000 μm, reaching about 14 mg·L·S·10. A small amount of NH-N was produced in 2000-6000 μm, which could be attributed to denitrification activity. There was no change deeper than 6000 μm, while NO-N was produced at a depth between 0 and 6000 μm and was consumed in the deeper zone. At the depth of 9000 μm, the NO-N consumption reached a maximum of 5 mg·L·S·10. The consumption of DO and NH-N, which corresponded with the production of NO-N in a specific microscale range within the sediment, demonstrated nitrification and denitrification activities. In addition, the time required for the diffusion of only DO, NH-N, NO-N, and NO-N was estimated as 14 days; however, in the practical, even after 60 days of operation, there was still a continuous reaction, which provided further evidence towards microbial activities within the sediment.