The control of grain drying process in grain dryers presumes the regulation of quantity of heat supplied to grain in drying chamber, which depends on moisture, temperature and the stage of grain drying. In the case of a dryer’s continuous running it is technically more sim-ple to regulate the quantity of heat with the help of speed change of discharge of grain from drying cham-ber, for this it is necessary to know the flow characteris-tics of a discharge unit. The aim of the research is to get mathematical model of dependence of flow rate of grain for a discharge unit of grain dryer on its design parame-ters and modes of operation. The research objectives are the creation of experimental facility of discharge unit of grain dryer and study of its flow characteristics by the methods of experimental design. The experiments were made with wheat grains on the experimental facility, simulating a discharge unit of shaft and tower driers. Experimental installation turns on the bunker which out-let is blocked by the mobile plate set in back and forth motion by electric motor with a reducer. The frequency of rotation of the engine is controlled by frequency con-verter. As the parameters influencing the efficiency of discharge unit the clearance between the edge of outlet of the bin and the movable plate, oscillation frequency of the covering plate and moisture of grain are accepted. Required model is the result of realization of complete factorial design 23. The analysis of received depend-ence allows to conclude that the frequency of fluctuation of blocking plate and humidity of grain have the strong-est impact on productivity of unloading device. The im-pact of the clearance between the edge of the bin and covering plate is not significant, so the regulation of flow rate of grain through discharge unit by the way of changing clearance is not rational, from technical point of view it is simpler and more effective to regulate the flow rate by changing oscillation frequency of covering plate.