Abstract: Abstract: Suspension velocity of agricultural material is important basic data for the research of technology and equipment for mechanical cleaning. Given the characteristics of threshed materials to be cleaned of crops harvested by combine harvester, based on the suspension principle of material and the characteristics of mechanical cleaning working condition, we designed a kind of vertical air sweeping suspension velocity testing device for agricultural material. This device mainly consists of 3 kinds of components, including the air force and its controlling components, the flow field structural components and the measuring components. The air force and its controlling components are directly connected with the flow field structural components by flanges in vertical direction, and the measuring components are installed on the flow field structural components. The structure is compact. The air force and its controlling components consist of the centrifugal fan, the frequency converter, the conduit coupler between fan and pipelines, and the protecting net. The flow field structural components consist of the grille tube, the airflow-smoothing grille, flanges, holding net for materials, entrance gate of materials, collecting board for materials, lower airflow-stablizing pipe, tapered observation pipe, upper airflow-stablizing pipe, obstructive net for materials, and so on. The measuring components consist of the L type Pitot tube, bracket of Pitot tube, intelligent pressure air-volume anemometer, air conduit, suspended height ruler, observation platform, and so on. The overall size of this device (length × width × height) is 1.8 m × 1.1 m × 4.2 m. The motor power of fan is 7.5 kW. The airflow velocity can reach 40 m/s in this device. The flow field structural components are mainly formed by the grille tube, lower airflow-stablizing pipe, tapered observation pipe and upper airflow-stablizing pipe connected successively via flange connections in vertical direction. The 4 pipes are all welded with flanges at both ends and made of polymethyl methacrylate. The lengths of the 3 pipes except the grille tube are all 1 m. The inner diameters of the grille tube, lower airflow-stablizing pipe and the small end of the tapered observation pipe are all 240 mm. The dip angle of tapered observation pipe is 4° and its inner diameter of big end is 380 mm. We designed a circular airflow-smoothing grille installed in this device to avoid generating eddy at the outlet of fan, and its height is 100 mm, the side length of its square hole is 30 mm, and the thickness of grille plate is 2 mm. The anemometer can display the temperature, humidity, pressure, airflow velocity and flow rate in real time in the measurement. We designed and conducted staged suspension experiments to measure the suspension velocity of each component of the threshed materials to be cleaned by combine harvester during the harvesting time of foxtail millet, buckwheat and oat, respectively. The results show that the range of suspension velocity of grains, spikelets, stalks and leaves of threshed materials to be cleaned of foxtail millet is respectively 4.29-8.88, 1.03-6.48, 1.71-6.09 and 1.03-3.09 m/s. The range of suspension velocity of grains, ramulus, stalks and leaves of threshed materials to be cleaned of buckwheat is respectively 4.47-10.18, 1.85-5.18, 2.80-8.37 and 0.76-2.99 m/s. The range of suspension velocity of grains, testas, ramulus, stalks, leaves and unpeeled grains of threshed materials to be cleaned of oat is respectively 4.35-11.01, 0.62-1.71, 1.62-4.52, 1.14-6.28, 0.91-3.56 and 3.24-9.48 m/s. The grains' suspension velocities of foxtail millet and oat are both different from their most light impurities', the grains' suspension velocity of oat is similar to its unpeeled grains', and the grains' suspension velocity of buckwheat is different from its minor light impurities'. This study can provide reference for the research and development of cleaning technology and equipment for agricultural materials.