Threshing is an essential and very important working procedure of rice combine harvest. The traditional threshing device has shortage in threshing capacity when harvest high yield rice, thus new type threshing device need to be developed to solve the problem.

　　Tests of connection forces between grain and petiole of four kinds of high yield rice including hybrid rice Yongyou 12, hybrid rice Yongyou 9, japonica rice Jiayou 2 and glutinous Yongyou 11 have been done. The distribution spectrum of grain connection force was drawn. The results showed that the connection force in different positions on rice spike varied widely with variant coefficient in the range of 37.1%—77.7%. The distribution of grain connection force of hybrid rice Yongyou 9 was wide but the average value was intensive. It is beneficial for selection of cylinder speed.

　　Based on the calculation of the threshing coefficients of four kinds of high yield rice, mathematical models of the relationship between the average connection force of grain with the top gear line speed and the rotational speed of the threshing cylinder were established and validated, which provided the theoretical basis for the differential-speed threshing technology. The results showed that the top gear line speed and the rotational speed of bow tooth differential-speed threshing cylinder should be selected between 9.91 m/s to 17.86 m/s and 400—720 r/min, respectively, the top gear line speed and the rotational speed of rod tooth differential-speed threshing cylinder should be selected between 800 r/min and 1 440 r/min.

　　Bow tooth differential-speed threshing cylinder and rod tooth differential-speed threshing cylinder were developed, which were used in head-feed rice combine harvester and full feeding rice combine harvester respectively. In order to verify the performance of differential-speed threshing device, contrast experiments of differential-speed threshing cylinder and single speed threshing cylinder were conducted. Distribution of mixture after threshing of different kinds of threshing device was analyzed and the components of mixture after threshing were surveyed. The results showed that the differential-speed threshing device relied on the low threshing speed to reduce the grain and stalk crushing, and relied on high threshing speed to reduce un-threshing loss. The performance indexes of loss rate, crushing rate, impurity rate of differential-speed threshing device had been effectively improved.

　　The study provides a theoretical basis and practical reference for threshing device optimization of combine harvester.