In the experimental system of diffused laser light field pumped sharp angle incidence laser light probing small cesium beam frequency standard, the light frequency shift (mainly the AC Stark shift) caused by diffused laser light comes from the diffused laser light field, and the light frequency shift caused by fluorescent light comes from the pumping region have been measured carefully. The measured results were analyzed and compared with the calculated results. The results proved that, under normal working conditionin, the light frequency shift caused by diffused laser light is less than -2×10-13, the light frequency shift caused by fluorescent light is about 0.8×10-13, such results are acceptable for a small optically pumped cesium beam frequency standard.