Abstract: Driving dentate disc is the power source of mechanical bale knotter. The bale knotters used in domestic mostly depend on imports and the knotters could not meet the requirements of high-efficient straw belting due to the unstable working status caused by un-smooth cam working surface of driving dentate disc and discontent with static equilibrium. This paper took the D-twine knotter as the research objective and optimal designed a weight driving dentate disc with the features of high surface quality and stable transmission based on the theory of reverse engineering. Through the analysis of the working principle of D-twine knotter, the paper reconstructed the 3D driving dentate disc and optimized its surface and structure with the Imageware and Pro/E software. The analysis of multi-surface continuity and surface contour of driving dentate disc showed that after the optimization of weight driving dentate disc, its surface position deviation and change rate of tangent were 0.0013-0.0037 mm and 0.1393°-0.1400°, respectively. The change of surface curvature was continuous and the chord deviation was 0.100 mm, indicating the disc surface met the requirements of A-class surface. Furthermore, the parts matched with disc surface worked steadily, which ensured the operation order in straw-belting. The new center of the disc was about (2.87, 0, 0) mm, which reached the requirements of static equilibrium and could meet the requirements of high-speed belting in heavy straw cover fields in harvest season in China.