Abstract: Abstract: To study the effect of threshed mixture feed quantity of combine harvester threshing device on the cleaning device's airflow field, a multiple-duct cleaning test-bed was developed. This test-bed included variable feeding device, multiple-duct cleaning device, transmission device, frame and control cabinet. The test-bed could adjust threshed mixture's feed quantity, fan rotation speed, vibration sieve opening, wind-board dip angle and other parameters. Also, through controlling discharge outlet opening and electromagnetic feeder frequency, the feed quantity could change (1-4 kg/s). Moreover, the test-bed could automatically save the data and display the data on the computer screen. The test-bed was used for further study on the internal airflow field under various working conditions. In this study, 25 airflow velocity measuring points were arranged above and below the vibration sieve in the cleaning room. The feed quantity of non-material and 1-4 kg/s was tested by VS110 type hot-wire anemometers under rated conditions in which the fan speed was 1350 r/min, the vibration sieve opening was 22 mm, the dip angle of Wind-board I was 24°, and the dip angle of Wind-board Ⅱ was 20°. The traditional hot-wire anemometer was easy to be damaged by material impact, but the anemometer in this study could avoid the problem, and furthermore, its measuring accuracy was higher. In single test, 10 hot-wire anemometers were used to measure the airflow velocity and save the data. Test experiment showed that the airflow velocity of each measuring point decreased with the increasing of feed quantity of threshed mixture; in the non-material case, the airflow speed arrived maximum. With every 1 kg/s feed quantity that was increased, the airflow velocity decreased by 1.2%-16.4% at the top of the vibration sieve. The airflow velocity decreased by 1.4%-9.3% at measuring point under the vibration sieve. Especially in 4 kg/s feed quantity that was the maximum quantity, the airflow velocity above the tail of the vibration sieve was more attenuated, which decreased by 12.6%-30.7% compared with non-material. Under the same feed quantity, the airflow velocity at the transverse 1/3 and 2/3 position of the vibration sieve was larger than that at the 1/2 position, which was caused by the multiple-duct centrifugal fan structure. The airflow velocity of the front above the vibration sieve at longitudinal direction was smaller and the airflow velocity in the middle and posterior was larger and the airflow velocity picked up in the end of vibration sieve; for the front position above the vibration sieve was only affected by the upper air-duct, while the middle part was influenced by the lower air-duct of multiple-duct centrifugal fan, and the sieve surface tail was close to the exit of the machine and the cut area suddenly changed small to cause the airflow velocity rising. The research provides the basis for the design of multiple cleaning devices and the adjustment of parameters in the field experiment. In the actual harvest operation, when the crop feeding quantity increases, appropriately increasing the fan speed or reducing wind-board dip angle is necessary in order to enhance the air stripping and stratification ability, and it also can guarantee the cleaning quality and efficiency.