To improve the ditching performance of high-firmness grassland, a bionic root cutter based on the contour curve model of Prosopocoilus astacoides' jaw was designed, as well as a grassland root-cutting and ditching device combining the bionic root cutter with the core-share opener. The grassland ditching experiment investigated the horizontal working resistance, ditching stability, and soil disturbance of the three ditching parts. According to the trial results, when the core-share opener was used for ditching in high-firmness grassland, the ditching stability was poor, the working resistance was high, and the grassland was severely damaged. Compared with the independent configuration of the core-share opener, the ditching performance can be significantly improved by installing a root cutter in front of the core-share opener, and the effect of installing the bionic root cutter was better than that of an ordinary triangular root cutter. When the ditching depth was 5 cm, 10 cm, and 15 cm, the ditching stability coefficient of the root-cutting and ditching device increased by 16.67%, 9.54%, and 6.18%, respectively, the horizontal working resistance reduced by 58.73%, 28.15%, and 19.84%, respectively, and the soil disturbance area reduced by 30.58%, 23.73%, and 20.21%, respectively.