A system for synthesizing a real-time image by using optical surface motion signals includes: an acquisition unit configured to acquire an image of a patient before treatment and real-time optical surface data of the patient during treatment; and a synthesis unit configured to synthesize the acquired image of the patient before treatment and the real-time optical surface data of the patient during treatment into a real-time image that is synchronized with a change of the optical surface motion signals according to a certain mapping relationship. The synthesized real-time image achieves precise, real-time, non-invasive, visual dynamic tracking of the moving target volumes without concomitant dose during radiotherapy on the existing traditional accelerator platform.