To address the issues of incomplete threshing, separation loss, and grain breakage during the harvesting of super hybrid rice with conventional threshing and separating units in head-feed combine harvesters, a segmented-differential threshing and separating unit was developed. This unit mainly consists of a coaxial segmented-differential threshing drum and a rotary concave screen. Its structure and working principle are described in detail. A three-factor quadratic regression orthogonal rotation combination test was conducted, with the rotational speed of the segmented-differential drum, the linear velocity of the rotary concave screen, and the clamping chain speed as test factors. The grain loss rate, breakage rate, and impurity rate were taken as performance indicators. The test results were analyzed using Design-Expert 8.0.6 software to establish a mathematical model for the performance indicators and to determine the optimal combination of working parameters. Additionally, a comparative test was carried out between the segmented-differential unit and a conventional single-speed unit. The results showed that when the rotational speed of the low-speed/high-speed drum in the segmented-differential unit was 520/630 r·min-1, the linear velocity of the rotary concave screen was 1.20 m·s-1, and the clamping chain speed was 1.10 m·s-1, the grain loss rate, breakage rate, and impurity rate were 1.95%, 0.20%, and 0.56%, respectively.