Conveyor cleaning represents working body of a combine harvester consisting of giving conveyor, the fan and conveyor sieve with cattle board. A conveyor sieve is trellised a grate conveyor (conveyor) consisting of separate trellised sections each of which fastens to pads of two closed contours of a special conveyor chain screws. Separated heap enters the upper branch of the lattice conveyor, where its separation takes place, and the passage fraction of the heap arrives at the sloping board, from which it is raked by the lower branch of the conveyor sieve into the grain auger of the combine. The quantity (layer thickness) of the lots processed by unit of area of separating sieve surface depends on linear speed of a conveyor sieve. Proceeding from the results of research by Professor S.A. Alferov that the separa-tion of small grain heap on the grinder of the combine can be lost without loss, if the grain heap layer exceeds 3-4 cm, mathematical expressions are derived analyti-cally to determine the optimum value of the linear veloci-ty of the conveyor screen for cleaning the combine har-vester, which provides the required thickness of the layer of the heap to be treated this sieve. Using the ob-tained mathematical expressions, calculations were made of the optimum speed of the conveyor sieve for different values of the heap feed for cleaning (from 1 to 10 kg / s) and various densities of this heap (γv = 120-240 kg / m3). According to these calculated data, the graphs of linear velocity variation are constructed de-pending on the second pile supply and its density for combines with a threshing width of 1200 and 1500 mm. Analyzing received mathematical dependences and schedules, one can come to the conclusion that the more the supply of heap for cleaning and the less its density, the higher values are required for the linear speed of the conveyor sieve. On the other hand, the smaller the feed amount and the greater its density, the lower the sieve speed required.