Ultra-smooth surface is widely used in aspheric optics elements and astronomical instruments. Fabrication of ultra-smooth surfaces, especially for hard and brittle materials, has always been a challenge to the optics industry. To efficiently produce ultra-smooth surfaces, a novel disk hydrodynamic polishing (DHDP) is proposed. As a non-contact hydrodynamic polishing method for DHDP process, the polishing tool rotates at high speed under the drive of the motor. At this time, a hydrodynamic fluid film is formed between the polishing tool and the workpiece surface. In the gap of fluid film, the velocity and pressure of fluid show a regular gradient, and it drove the solid particles impact the workpiece. Then, the computational fluid dynamics(CFD), solid-liquid discrete phase model (DMP) and erosion model (EM) are combined to track the particles trajectories in the proximity of the workpiece and reveal the erosion theoretical mechanism for DHDP process. The current research has a great significance to analyze the characteristics of the complex interactions between the phases and the erosion of solid particles in DHDP process. The simulation results can also be used to quantitatively predict the local erosion depth on polishing surface.