Bonnet polishing is widely used in final processing of optical elements, as the bonnet tool has the characteristic of fine surface adaptability and controllable pressure. For the purpose of ensuring the stability and exact controllability of polishing process, it is necessary to make precise dressing of bonnet tool. In this paper, first a dressing scheme using cup diamond wheel is proposed for bonnet tool, and then the feasibility of the dressing scheme is verified by analyzing the trajectory and the envelope of the diamond particles on the cup wheel. After that, the influences of the dressing process parameters on the dressing efficiency and trajectory distribution are defined through theoretical analysis and MATLAB simulation, and by simulation the dressing process parameters are determined. In addition, a trimmed program with variable speed ratio is proposed to homogenize the dressing tracks. Finally, an experiment was conducted to test the simulation result. This paper provides the theoretical basis for actual dressing process of the bonnet tool.