Abstract: Based on computational fluid dynamics (CFD), the flow field simulation results of four schemes of a Suzhou environmental protection company's experimental downdraft fabric baghouse filter were analyzed and compared, in no deflector (scheme 1), straight plate with isotropic wing plate (scheme 2), straight plate with anisotropic wing plate (scheme 3), and vertical deflector with rectifier grille (scheme 4). The relative standard deviation of cross-sectional velocity at the first 100 mm of the bag inlet was selected as the evaluation index. The feasibility of differential pressure, flow velocity and concentration as the characteristic factors for leak detection was studied by numerical simulation of bag breakage in different areas. The results showed that the flow field distribution of scheme 4 was the most uniformed, better than schemes 2 and 3; scheme 2 had the smallest resistance increase, significantly lower than schemes 3 and 4. The study verified that the small-scale broken bag outlet concentration was linearly positively correlated with the broken bag area through simulation, and found that the pressure difference and flow rate, as the characteristic factors of leak detection, had no significant effect, and the concentration change was the most sensitive. Combined with the two important evaluation indicators of airflow distribution uniformity and resistance, the speed uniformity index of scheme 2 was 0.36, the speed uniformity index of scheme 4 was 0.2, the increase of resistance of scheme 2 was much smaller than that of scheme 4, and scheme 2 was more practical. The numerical simulation scheme provided in this paper could provide a certain reference for the distribution of the deflector plate of the lower intake bag filter and the selection of the monitoring sensor.