The invention discloses a device and a method for treating nitrogen-containing waste sewage by using a down-flow integrated nitrification and denitrification aeration biological filtering device in the technical field of sewage treatment. The invention provides a novel biological filtering device for efficiently removing nitrogen, wherein a gas-water separating device is arranged at the middle of a biological filtering pond and is used for dividing the biological filtering pond into a nitrification zone and a denitrification zone. The invention also provides a method for efficiently removing nitrogen. According to the down-flow operation mode, the nitrogen-containing sewage and wastewater and the reflowed nitrifying liquid are simultaneously pumped into a denitrifying zone and nitrate nitrogen is reduced into nitrogen gas by using a carbon source in water; water subjected to nitrogen removal is nitrified in the nitrifying zone; ammonia nitrogen in water is oxidized into nitrate nitrogen; and mostly effluent in the filtering pond is reflowed to the denitrifying zone and provides an electron acceptor for the denitrifying zone, thereby efficiently removing organic matters, nitrogen and suspended matters in the nitrogen-containing waste sewage. According to the device and the method disclosed by the invention, efficient nitrogen removal of the nitrogen-containing sewage and wastewater is realized in the same biological filtering pond; high quality of effluent and long back flush period are obtained; energy consumption is low; and the occupied area is effectively saved.