Abstract: Castor has been one of the most important chemical raw and strategic materials in the aviation, chemical industry, automobile, fragrance, and medicine. The annual output of castor capsules is less than 200 000 tons, while the annual demand is more than 400 000 tons in China. Therefore, it is extremely urgent for the mechanized production of castor, particularly on the harvesting in recent years. In this study, a disc-cutting picking device was designed for the castor, according to the physiological characteristics of castor plants. The device was mainly composed of the frame, double-disc cutting, capsule recycling, feeding auger, and transmission system. The disc-cutting mechanism was first utilized to separate the castor plants, and then the plant was transported on a conveying device into the cleaning section for cleaning. An optimal combination of parameters was finally achieved for the smooth cutting free of loss, where the speed and motion trajectory were determined for the disc-cutting mechanism. Some parameters were also designed, such as the rotational speed, the radius, and the installation center distance of the cutting disc. A smooth transportation without the picking loss was implemented to quickly transfer the castor plant from the cutting mechanism to the feeding auger. A clamping force of the castor plant was calculated to determine the clamping height, spacing, and working speed of the dial-tooth chain. The structural parameters of the capsule recycling mechanism were designed to avoid the dropping from the cutting device under the vibration of the harvester. An orthogonal test was carried out with the type of cutting disc, the rotational speed of the cutting disc, and the forward speed of the harvester as the test factors, while the stubble altitude difference and picking loss rate as the indexes. The results showed that an optimal combination of parameters for the stubble altitude difference was the waved-type of the disc, the disc rotational speed was 800 r/min, and the forward speed was 0.8 m/s. The type of the disc also presented a significant effect on the stubble altitude difference, but not so the disc rotational speed and forward speed. Meanwhile, the optimal picking loss rate was obtained under the waved-type structure of the disc, where the disc rotational speed was 600 r/min, and the forward speed was 1.1 m/s. There was a significant effect of the disc rotational speed on the picking loss rate, whereas, there was a very significant effect of the disc type and forward speed. Taking the picking loss rate as the main index, the integrated balance was used to determine the operating parameter, where the structure type of the disc was waved-type, the disc rotational speed was 600 r/min, and the forward speed was 1.1 m/s. A field test was carried out to verify the data. It was found that the average difference of stubble altitude was 0.85 mm, the average picking loss rate was 3.13%. The waved-type cutting disc can be an ideal cutting tool for the castor stalk with even stubble heights, indicating an excellent cutting performance, a lower loss rate, and stronger field adaptability. The finding can provide a strong reference for the development and design of castor harvesting equipment, together with the rice or corn combine harvester.