A　lab-scale　two-stage　UASB-A/O　combined　process　for　treating　the　real　municipal　waste　leachate　is　used　to　investigate　the　inhibition　kinetics　of　free　nitrite　acid　(FNA)　to　denitritation　using　nitrite　as　electron　acceptors　in　wastewater.　Under　the　premise　of　achieving　short-cut　nitrification-denitrification　stably　(running　130　days),　a　number　of　denitrification　batch　tests　are　carried　out　in　different　concentrations　of　NO2--N　and　under　different　pH　gradient　with　sludge,　which　is　from　an　A/O　reactor　and　has　good　biological　short-cut　denitrification　nitrogen　removal　efficiency.　A　denitritation　inhibition　kinetics　model　is　established　based　on　a　large　number　of　experiments　and　the　Nitrous　denitrification　inhibition　kinetic　constants　under　different　pH　are　deduced　by　function　match.　The　relationship　curves　of　NO2--N　concentration　and　specific　rate　of　denitrification　match　the　Andrews　inhibition　kinetics　model　well　at　constant　temperature　and　pH　conditions.　The　maximum　specific　denitrification　rate　Rmax　and　half-saturation　constant　KS　significantly　vary　at　different　pH,　Rmax　and　KS　being　17.8　mg/(g·h)　and　6.40　mg/L　under　pH　8.0,　respectively.　When　pH　is　in　the　range　of　6.5-8.0,　the　inhibition　constant　KI　significantly　increases　with　the　increase　of　pH.　However,　the　corresponding　value　of　ρ(FNA)　(0.177-0.225　mg/L)　remains　the　same　level　of　magnitude,　which　proves　that　FNA　is　the　true　inhibitor　from　the　view　of　kinetics　point.