Selective catalytic reduction (SCR) denitrification is an urgent need for deep emission reduction of flue gas NO_x in cement kiln. In this paper, the SCR denitrification reactor of a cement kiln with a flue gas treatment capacity of 10 000 Nm³/h was taken as the research object, and the computational fluid dynamics (CFD) numerical simulation was used to analyze and compare the different distribution modes of the reactor inlet, and the flow field optimization method in the reactor was discussed. The results show that the reasonable installation of guide plate in the middle and gradual expansion section of the reactor flue inlet, and the installation of porous uniform distribution plate at the top entrance of the reactor have excellent flow field homogenization effect. The installation of porous uniform distribution plate plays an important role. Through the optimal combination of the homogeneous distribution device, the relative standard deviation C_v of the velocity above the top layer catalyst bed in the reactor reaches 8.45%, the maximum incidence angle is 9.53°, and the overall resistance of the system increases by only 37 Pa. Furthermore, when the reserved layer of the catalyst bed is placed in the top-level design can obtain the better optimal effect of flow field, and C_v of speed can be reduced to 6.73%. This paper is expected to provide reference for further optimization design of SCR denitrification reactor of cement kiln.