To investigate the effect of explosion discharge duct on the flame propagation of dust explosion under the condition of high opening pressure, the dust explosion discharge process of 20 L spherical device was simulated by FLACS software. The effects of different duct length (0 ~ 10 m) and duct diameter (50 ~ 130 mm) on the flame shape, temperature and length during dust explosion discharge were studied. The results show that increasing the length of venting duct can reduce the temperature of discharge flame; After installing the explosion discharge duct, the shape of the discharge flame front of dust explosion changes from "semi arc" to "knife edge", and the maximum discharge flame length suffers significant impact; Furthermore, when the diameter of the duct is small, the longer the duct length is, the shorter the discharge flame length is; When the diameter of the duct is large, the discharge flame length first increases and then decreases with the increase of the duct length.