The invention discloses an automatic polishing system and method. The automatic polishing system comprises a robot, a burnishing head and a polishing control system, wherein the burnishing head is located at the front end of a mechanical arm and is particularly mounted at the front end of the mechanical arm in a telescopic floating manner by virtue of a constant force control device; the constant force control device comprises a base, a guide groove, a sliding block and an elastic part; the burnishing head is fixedly connected with the sliding block and is driven to float in a flexible manner by the sliding block. According to the automatic polishing system, the burnishing head is connected with the mechanical arm of the robot by virtue of the constant force control device, so that the burnishing head can float; furthermore, a burnishing force applied to workpieces by the burnishing head is maintained at a constant value by virtue of a constant force elastic component, so that the whole machining process can be finished in a constant force polishing mode, the shortcoming of inconsistent qualities of polished surfaces caused due to low repeated positioning accuracy of the robot is made up, the requirements on the repeated positioning accuracy of the robot are reduced, the polishing consistency of the surfaces of the workpieces is guaranteed, the machining quality is improved, the rejection rate is decreased, and the polishing efficiency is improved.