The invention discloses Citrobacter werkmanii for degrading ammonia nitrogen and application thereof. The strain number of Citrobacter werkmanii is Ad-5, and the preservation number of the strain preserved in the China General Microbiological Culture Collection Center is CGMCC No. 14562. The Citrobacter werkmanii Ad-5 can degrade high-concentration ammonia nitrogen in sewage, garbage leachate andbad smell, has good ability of treating polluted sewage, garbage leachate and bad smell with high content of ammonia nitrogen, can effectively solve pollution of sewage, garbage leachate and bad smell, and is used to makes contribution to environmental governance.