Fluent software was used to simulate the flow field in the selective catalytic reduction (SCR) denitrification reactor, based on the standard k-ε model, porous media model, material transport model, DPM model. A single gas phase flue gas was used to analyze the effects of different rectifying grids spacing, rectifying grid height, rectifying grid position and baffle number, baffle angle on the uniformity of the flue gas flow field. The influence of the smoke with different components in a single gas phase under the optimal scheme can be concluded. The gas verified under different loads, as well as different loads under DPM dual-phase coupling conditions. The results showed that the maximum incident angle was less than 90° from the absence of the rectification grid to the addition of the rectification grid, and the vortex above the catalyst disappeared. When the spacing of the rectifying grid was 107 mm, the height of the rectifying grid was 200 mm, and the rectifying position was flushed with the lower edge of the entrance, the velocity distribution deviation coefficient at 100 mm of the upper layer of the first catalyst layer reduced to 19%. When the number of baffles was 7, and the baffle angle was 18.2°, the most suitable situation, the velocity distribution deviation coefficient at 100 mm above the first layer of catalyst was 11.91%, and the maximum incident angle was 3.14°. When the flue gas with different components in a single gas phase and different loads were simulated under the best parameters, it met with the engineering requirements. Using DPM two-phase coupling, comparing the particles with a single gas phase under the Rosin-Rammler distribution condition, it was found that the average velocity at 100 mm above the first layer of catalyst increased to a certain extent, the velocity standard deviation had a small change, and the velocity distribution deviation coefficient was correspondingly reduced.