Abstract: The lower operating temperature of SCR denitration reactor directly caused catalyst deactivation. In order to resolve this problem,taking the typical SCR denitration system of 600 MW coal- fired unit as research object,the influence of reaction temperature,NH3HSO4 formation temperature in catalytic reaction region,sprayed ammonia diluted wind and permissible error of temperature measurement components on the temperature of denitration area was analyzed. The minimum safe operating temperature of SCR denitration reactor was determined. The results showed that,the activation temperature of vanadium- tungsten- titanium catalyst ranged from 320 ℃ to 420 ℃. When the temperature was between 340 ℃ and 380 ℃,the reaction had the best performance and the denitration efficiency reached about 90%.The condensation temperature of NH3HSO4 which was the major component in gas phase was between 270 ℃ and 320 ℃. The sprayed ammonia diluted wind reduced the denitration temperature by 2. 6 ℃ to 2. 9 ℃. The permissible error of temperature measurement components had relatively fixed influence on SCR denitration reactor,the maximum reduction was about 4 ℃. At last,the inlet temperature was determined in the range of 350 ℃ and 390 ℃.