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Aiming at the problem of soil tillage erosion (soil migration from the higher side of the sloping land to the lower side) and its unknown mechanism during the contour rotary tillage operation of the slopes in the hilly and mountainous areas of the Loess Plateau. Through the combination of theoretical analysis, simulation test, soil trough and field test, the research on the erosion mechanism of rotary tillage by hillside tractor on sloping land was carried out in depth. Firstly, the parameter equation of soil disturbing volume of H245 standard rotary blade under sloping conditions was constructed, the classical mechanical analysis of the soil disturbing process of the rotary blade was completed, and the main influencing factors of soil erosion were determined: tillage depth, rotary blade shaft speed and rotary tillage forward speed. Then, based on the EDEM simulation software, the soil disturbance law of a single rotary blade and the whole rotary cultivator was studied, and it was concluded that the soil particles moved backwards under the dynamic sliding action of the side cutting edge of the rotary blade. The displacement of soil particles in the shallow layer was the largest, the displacement in the deep layer was the smallest, and the displacement of soil particles in the deep layer near the rotation center of the rotary blade was the largest. The lateral displacement direction of soil was affected by the direction of the tangential edge of the rotary blade, and the bending angle of the tangential edge largely determined the lateral throwing effect of soil particles. The vertical position of soil particles showed a trend of becoming deeper and then shallower as the rotary blade was immersed in the soil. Finally, the single factor and orthogonal tests of rotary tillage were carried out on the spot with the rotational speed of the rotary tiller shaft, the rotational tillage speed and the slope angle as the test factors. The single factor test obtained the law of soil horizontal and lateral displacement changing with the above three factors. The variance analysis of the orthogonal test showed that the factors affecting the lateral displacement of the soil were the slope angle, the rotational speed of the rotary tiller shaft, the speed of the rotary tillage, and the factors affecting the horizontal displacement of the soil were the speed of the rotary tillage, the slope angle, and the rotational speed of the rotary tiller shaft. The regression equation between the soil lateral displacement, the horizontal displacement and the independent variables was obtained by fitting, and the optimal operating parameters combination of the rotary tiller was determined under the five setting slope angles through parameter optimization. The research result can provide good technical guidance for the high-efficiency and low-erosion operation of the existing rotary cultivator in the sloping tillage area of the Loess Plateau, and it can also provide research ideas for the innovative design of the subsequent rotary cultivator for sloping land.