Abstract： Experiments on the conveying characteristics of Inner Mongolia bituminous coal powder were conducted on a pilotscale pressurized pneumatic conveying test rig. Effects of operational conditions and material properties on the voidage ε were explored respectively. The results indicate that increasing the conveying pressure p is beneficial for conveying at a lower ε. ε initially drops and then grows with the rise in the flow rate of fluidizing gas Qf. Increase of supplemental gas Qsp leads to a higher ε. With the increase of total differential pressure Δp, ε of 52 μm coal decreases at first and then increases marginally, whereas the voidages in the riser section εr of 115 μm and 300 μm coal both rise continually. εr of pulverized coal with larger particle size exhibits a lower voidage at the same Δp. Increase of the moisture content  M of coal results in a lower volumetric flow rate of solids and a higher volidage of the two phase flow. With the decrease of superficial gas velocity Vg, the flow regime of 300 μm coal changes from suspended flow to slug flow, while the volidge in the pipeline εp declines gradually.