Burden distribution mode determines the burden porosity, and the burden porosity determines the secondary distribution of gas flow. In this paper, a threedimensional mathematical model was employed to study the change of pressure drop and gas flow in shaft furnace under different singleloop charging gear (0.0, 0.8, 1.6, 2.0, 2.4, 2.8 m in radius of charging tip round). The results showed that the burden size segregation has great effect on gas flow distribution during charging process, and the gas flow rate is very low on the tip of stock pile. With the outward motion of charging gear, the pressure difference of the whole shaft furnace and bustle increase. The gas flow backwards slightly decreases at first but rapidly increases. The inflexion appears in 2.0 m charging gear. The suitable charging gear is 1.6 m, and should not exceed 2.0 m.