During the operation of the SCR denitration system, there is a widespread problem of poor uniformity of flue gas temperature after heating in internal combustion furnace. At present, the method of shielding the font section of the burner and adding a deflector in the rear section is widely used in China to improve the temperature uniformity in the inlet section of the SCR reactor, and how to properly set the diversion device in each section is difficult. In this paper, the FLUENT numerical simulation method is used to study the influence of the setting position of the burner and the arrangement of the front and rear diversion devices on the temperature field of the system. At the same time, the reliability of the simulation results is verified by combining the test results of typical engineering operations. The results show that after optimizing setting position of the deflector and the front and rear section diversion devices, the temperature deviation of the import section of the SCR reactor can be reduced to less than ±5 ℃, and the system resistance can be controlled within 300 Pa.