This invention discloses a technique for garbage buried treatment with denitrification in site. In a nitration reactor, there are: an upper layer-aeration zone having aerator, a medium layer-facultative zone and the bottom layer-anaerobic zone. In the aeration zone, ammonia is oxidized into NO3-by the autotrophic nitrifier; in the facultative zone, NO3-is reduced into N2 by denitrifying bacteria by using organic substances as electron donor, and the N2 is released into the air to achieve the transformation from NH4 to N2 and its removal. In the anaerobic zone, the organic matter is degraded into methane. This invention provides a biological reactor by using above-mentioned technique. In this invention, the three (buried main body, produced gas and liquid) is considered into an integral one, so having advantages of: low cost, high efficiency.