It is a critical technology to improve the optical film uniformity during the film deposition process. The ion beam sputtering and polishing system was used to prepare the film on the surface of large-aperture optical elements. A calculation method for controlling the dwell time ratio I of the ion beam working at the center and edge of optical component was proposed. The dwell time ratio I was calculated by the film thickness data obtained from the center and edge, and the dwell time ratio I was revised step by step. Then it was input in the program as one of the sputtering process parameters. The experimental results show that, when I was revised to -26.6%, uniform film can be achieved on optical elements with a diameter of 300mm-600mm. Taking a Si film on the surface of fused silica as an example, the experiment was carried out for 6 hours. The film thickness is about 212 nm, and the film uniformity could reach up to 0.42%, which meets film thickness uniformity requirements by ion beam sputtering deposition method.