Abstract: In view of inadequate efficiency of cleaning device about axial flow type grain combine harvester that using threshing method，double fan oscillating screen type cleaning device was designed.And its front fan had three air ducts.During the experiment，a plurality of measuring points were set in the surface of cleaning sieve，flow velocity value of each measuring point was measured by anemometer.Airflow distribution of sieve surface was analyzed.Experiment results showed that the size and distribution of airflow from three air ducts of front fan could meet the needs about airflow distribution of cleaning device for longitudinal axial flow type threshing method.After fan could effectively assisted cleaning sieve discharge short stem，so as to improve the cleaning effect.