As Future emission limits of diesel engines is more stringent, model-based control strategy of selective catalytic reduction (SCR) is becoming necessary. Therefore, a catalytic converter mathematical model for simulating selective catalytic deNOx reaction is very important. In this paper, a one dimension catalytic converter mathematical model that consists of thermal energy model, SCR reaction model and NH3 storage model for simulating urea-SCR reaction process is presented. Based on this model, the impact of temperature and gas hourly space velocity (GHSV) on NOx conversion efficiency has been researched. According to the results of simulation, it shows good agreement with experimental data.