Abstarct: Reduction of nitrogen oxides can be by injection ammonia and using catalytic at the SCR method or just injection Ammonia or Urea at the SNCR method. Due to higher cost SCR method compared SCR method and transporting and storing Ammonia is more difficult than Urea, SNCR with urea injection method is more practical. Due to above reasons, to evaluate this method(SNCR With urea injection) and ways to increas its efficiency, wich is defined as ratio of percent of NOX reduction to initial NOX, discused. In this thesis, Nitrogen oxides control from output of an incinerator by one methods of NOX reduction wich called SNCR procesed with using urea injection by simulation in the Ansys Fluent have been done. This thsis has been validated with the result of Mr. Young-Il Lim which published 2009. Mr. Young compared error rates obtained from simulation of uniform and non-uniform diameter of injected droplets, with other experimental results. In this paper a three-dimensional model of secondary chamber combustion in an incinerator has been studied. In all previous studies, used combustion theory is Arrheniuse model. This model is not able to investigate the effects turbulence on the reaction rate. Combustion model used in this study is EDC (Eddy Dissiption Concept). This model is able to predict the effects of turbulence and ractions kinetic on the rate of reaction. The aim of this study was to investigate the effect of urea injection parameters such as temperature, droplets diameter, injected velocity and cone angle on nitrogen oxide emission at the normalized stoichiometric ratio (NSR) =1.8. result of evaluation of the parameters mentioned, Shows that changes in cone angle nozzle has no significant effect on the reduction of NOX. Increasing the inlet temperature injection is increased to reduce NOX. With increasing velocity of urea injection, NOX reduction increases but because reducing residence time consentration of isocyanoric acic and N2O increased. Increasing particle diameter, depending on the condition of the combustion chamber, it is possible to reduce or increase the NOX emmision. Particle diameter, the particle penetration, reaction temperature and reaction time is affected.