To solve the problem of threshing drum being jammed and low working efficiency in head-feeding combine harvester with the fixed grade concave threshing-separating unit, the rotary grate concave threshing-separating unit was designed. The rotary grate concave surface ran the same direction along cylinder arc of threshing drum. The dynamic differential equation was established by the force analysis of rice during being threshed. A test platform of the rotary grate concave threshing-separating unit was developed. The effects of three factors, such as the speed of threshing drum, the speed of grate concave and the speed of chain, on the four performance indexes, such as loss rate, broken rate, impurity content rate and threshing power consumption were investigated. The optimal structural parameters and operation parameters were explored by quadratics rotary orthogonal combination design experiment. The multi-objective optimization calculation was carried out. The results showed that the running rotary grate concave could effectively prevent the threshing drum from being jammed;the best combination of parameters was as follows: the rotating speed of the threshing drum was 550r/min, the speed of the grate concave was 1m/s, and the speed of the chain was 1.2m/s. Correspondingly, the three indexes of loss rate, breakage rate and impurity content were 2.14%, 0.2% and 0.6%, respectively. The field test showed that equipped with a rotary grate concave threshing and separating unit the head-feeding combine harvester of rice production could work in the whole fast level with no jamming of threshing-separating unit, and improve working efficiency by more than 30% than the fixed grate concave. Each performance conformed to the national standard. The research result provided a theoretical basis for the design of head-feeding combine harvester for high-yielding rice.