The separation device of 4LZ?0.8 small-sized harvester were developed to solve the problems of bigger cleaning loss and blocked by wet material. The developed device mainly consists of the material conveying mechanism, a winnower, the cyclone separation cleaning tube and the fan composition. The original scraper throwing mechanism is removed, and a hemisphere component separation was installed in the cyclone separation tube. The rice was feed into the cyclone separation tube along the radial direction instead of the tangential direction. By using the self-made cyclone separating cleaning tester, a mathematical model of the cleaning system was established by regression analysis using the winnower rotation rate, the suction fan speed and the distance between separating assembly and entrance as factors, and the grain clean-ratio and the cleaning loss as performance index. The combined kinematic parameters have been optimized. The results indicate that the grain clean-ratio of 98.93 % and the cleaning loss of 0.035 % could be achieved under the speed of 1 133 r/min, the suction fan speed of 2 609 r/min, and the height between separating assembly and entrance of 51 mm.