In the experimental system of the small cesium beam frequency standard with sharp angle incident laser light pumping and sharp angle incident laser light probing,the light frequency shift (mainly caused by AC Stark effect) caused by fluorescence from pumping region was calculated theoretically.The results show,the light frequency shift can be effectively reduced in the sharp angle laser light pumping scheme.In additon,a new method to measure the light frequency shift by changing the diffusing angle of the pumping laser light beam was presented in this paper.