The statistic proposes the analytical provisions and the experimental results of the throughput capacity of the threshing apparatus of grain harvesters, from the capacity of straw, grain, straw content, blockage of design characteristics. The threshing capacity is most significantly affected by weediness due to humidity, with a relative weediness of 0.05 bread weight, the capacity of the threshing machine is reduced by 2.5%, and with 50% weed by 16%. Loading of the threshing machine determines the productivity of the combine and fuel efficiency due to fuel consumption for harvesting 1 hectare, as well as threshing 1 ton of crop. The power of the combine engine is designed to perform work in extrem econditions, as a result, the average loadis 2/3 of full. During the operation of the combines, the time is only 45…50% of the total operating time of the engine. Underemployment of the engine leads to overconsumption of fuel. So, if the SMD-21M diesel at full operational power of 103 kW consumes fuel of 0.24 kg on 1 kW for an hour, at loading on 50% 51 kW s. specific fuel consumption increases by 41 g/kWh, or 17%, which corresponds to fuel consumption 2.1 kg/year.