Abstract: Multiple-factor studies to investigate the rethreshing and separating of stripped paddy mixture, which was obtained by the SG800 stripper made by Silsoe Research Institute, Britain and IRRI, Philippines, on a special experimental device has been undertaken.The significances of factors included; cylinder rotary speed, distance between concave bars, clearance between cylinder and concave, feeding rate, on the performance index of unthreshed rate, broken rate, gripping loss rate, trash rate and power consumption were obtained from analysis of variance. The optimum combination of the factor levels has been discussed.The material after rethreshing and separating was collected along the axial direction sector by sector underneath the concave and straw dischange end of the device. The components and the distribution of the performance index have been analysed, and the results can be applied as references for the selection and design of rethreshing device and other processing mechanism.