The invention discloses a miniature combine harvester which is good in harvesting quality. The miniature combine harvester comprises a body and a cleaning mechanism arranged on the body. The miniature combine harvester is characterized in that the cleaning mechanism comprises a cyclone separator arranged on the combine harvester, a shell of the cyclone separator is divided into a cylindrical part and a conical part from top to bottom in the axial direction, and helical impellers are axially arranged inside the cyclone separator; a vertically-upward air outlet and a transverse feed port are formed in the cylindrical part, a discharge port is formed in the lower end of the conical part, and vent holes are formed in the shell wall, close to the discharge port, of the conical part; the feed port is connected with an output port of a threshing device, and the air outlet is connected with an input port of the threshing device. Some cereal grain which is not plump and moves along with airflow can be secondarily cleaned, and the cereal grain is prevented from being discharged as impurities. Accuracy of impurity removal is improved, and the cleaning effect is improved.