Abstract: To optimize the design and confirm the optimal combination of the key parameters of weeding unit which is part of weeding machine, the structure and working principles of the weeding unit were analyzed. A multi-index orthogonal experiment of four factors (the working speed, the rotation speed of weeding unit as well as the number and installation radius of weeding tines) were carried out, and each factor had four levels. For optimizing the best operational parameters combination, the effects of the parameters of the weeding unit on its weeding performances were analyzed. The experiment result indicated that the number of weeding tines had significantly effect on the performances of the weeding unit. According to the analysis, the best scheme was: the number of weeding tines 12, and rotation speed 190 r/min, installation radius 170 mm, working speed 2.1 m/s. Under such working conditions, the wounded seedling rate, weeding rate, and seedling buried percentage were 4.41%, 73.1%, less than 3%, respectively. The results can satisfied with the agronomic requirements of weeding between seedlings in dry farmland.