Rotary tillage knives, the most critical component of rotary tillage machinery, are extremely susceptible to bluntness and even breakage, affecting the tillage efficiency and performance of rotary tillage machines. Although drag reduction methods can mitigate the breakage of rotary knives to a certain extent, the breakage mechanism of rotary knives due to impacts and chiseling in the soil cutting process remains unclear. Taking the existing rotary tillage knife based on self-excited vibration as a prototype, a coupled DEM-MBD (discrete element method-multi-body dynamics) simulation model is established to analyze the three-directional resistance of the rotary tillage knife during soil cutting from a microscopic perspective. Moreover, a strength analysis is carried out for the rotary tillage knife body based on the simulation data, verifying the feasibility of the theory of selfexcited vibration for the reduction of resistance and damage of rotary tillage knives. However, the root of the rotary tiller blade is susceptible to fatigue failure due to its discontinuous geometric structure and the influence of cyclic loading. Accordingly, reinforcement bars are welded at the root of the self-excited vibration rotary cutter, and a strength analysis of the reinforcement bars of different sizes and structures is carried out through the response surface test. The Pareto front principle is also introduced to select the optimization parameters. The maximum deformation and maximum equivalent force of the optimized self-excited vibratory rotary cutter are reduced by 52.6 and 46.8 percentage points compared with those of the traditional rotary cutter and 11.1 and 23.1 percentage points compared with those of the self-excited vibratory rotary cutter structure before optimization, respectively. Results of the real-machine test show that the average torque reduction rate of the optimized self-excited vibratory rotary cutter is 12.91% compared with that of the traditional rotary cutter under the optimal working speed. The tillage depth stability of the rotary tiller equipped with a self-excited vibration rotary cutter is 95.78%, and the soil breakage rate is 71.39%, thereby meeting the operating requirements. The results of this study have practical significance for improving the operating life of rotary tiller knives and a high reference value for the application of self-excited vibration theory in rotary tillage operation.