The invention discloses a laser frequency stabilizing method and optical system for improving performance of an optical pumping cesium beam atomic clock. According to the method, a detected fluorescence signal of the optical pumping atomic clock is divided into two paths, one path of fluorescence signal is input into a microwave cavity of the optical pumping atomic clock through a feedback deviation correction loop, and the other path of fluorescence signal is input into the spectrum input end of a laser frequency stabilization module; laser output by a laser device sequentially passes an isolator (1), a delay wave plate (6) and a polarizing beam splitter (7), and is divided into two beams, one beam is used as detection light and enters a light pumping atomic clock detection area, and theother beam is focused by a lens, enters an acousto-optic modulator (9) for frequency shift output and then collimated into parallel light by a lens, and the parallel light is used as pumping light andenters a light pumping atomic clock pumping area. According to the invention, only one AOM device is added, and two sets of complex saturated absorption spectrum light paths and one laser are omitted, so that the system complexity of the whole clock is reduced, the cost is reduced, and the system reliability is improved.