Abstract: To investigate the factors behind flowability of tobacco powder, the HR method and Jenike shear method were used to analyze the flowability of tobacco powder at different particle sizes and with different moisture contents. Furthermore, the observed effects on the flowability were analyzed in terms of the particle's microstructure. The results showed that: 1) The pore structure of tobacco powder was not developed. Its specific surface area was about 1 m²/g, the cumulative pore volume was only 0.002 cm³/g and the most probable pore size was mesoporous (2-50 nm). The agglomeration behavior of small particles was presented by high cohesiveness, and the roughness of large particles was characterized by a relatively larger internal friction angle. 2) The tobacco powder belonged to the Molerus Ⅲ type. The flow function of tobacco powder of different particle sizes ranged from 2 to 8, and 75 μm was the minimum size of particles in a flowable area. The increase of moisture content reduced the flow function of tobacco powder. 3) Tobacco powder with a particle size larger than 75 μm had a compressibility index less than 30 and an HR index less than 1.4, and well flowability. For tobacco powder with a particle size smaller than 75 μm, the compressibility index was between 30 and 50, the HR index ranged from 1.4 to 2.0, and its flowability was poor.