Abstract: To address the issue of chatter in slender grinding arbors with large length-to-diameter ratios during precision grinding of internal threads in planetary roller screw nuts, which leads to degraded machined surface quality, parameter optimization of a vibration-damping grinding bar based on particle damping technology was investigated. The discrete element method was employed to establish a particle contact mechanics and energy dissipation model, through which particle material, particle size, and filling ratio were simulated and optimized. The damping ratio of the grinding arbor was tested via hammer excitation tests to validate the simulation results, and the optimal parameters were determined to be lead particles of 1 mm diameter at a 90% filling ratio. Comparative internal thread grinding experiments were conducted using the grinding arbor with the optimized particle parameters. Results show that the damping ratio of the particle-filled grinding arbor is 2.03 times that of the unfilled arbor, and the surface roughness of the ground internal thread is reduced by 28.6%. The designed particle-damping grinding bar can effectively improve the surface quality of ground internal threads of nuts and provide technical support for precision internal thread grinding.