Two technical measures were adopted to increase dust-catching rate of the Blast Furnace (BF) gas gravity duster, installing funnel-type baffle and changing intake manifold from central tube to cone collector with roof intaking in the BF Gas Gravity Duster. The gas flow field and particle trajectory in gravity duster were 3 dimension numeric simulated by using software FLUENT. Similar to dust collector cyclone, simulation results show that it can also produce swirling in gravity duster after changing gas-injecting method; the forming of the gas flow dead-zone avoids emergence of second fugitive dust after setting the baffles, the collisions between dust containing gas and the baffle were the main factor to cause particle segregation. The solid particle trajectory is so complex and stochastic. The calculated separation efficiency was also well fitted the reported experimental data.