The grain dropped to longitudinal cleaning sieve from threshing unit mound in the right corner of the screen deck will block cleaning. The theory of non-uniform air-flow cleaning was put forward and the conical centrifugal fan, resource of non-uniform air-flow was designed. Theoretical analysis and experimental verification show that, as the diameter difference between the small-end and big-end of conical centrifugal fan, the wind pressure difference of non-uniform air-flow forms, which results in high transversal wind velocity in the front of vibrating screen (the highest velocity is 2.6m/s). The wind pressure difference puffs falling grain to the other side, which changes initial distribution apparently and improves cleaning quality of transversal axis-flow feed combine.