Abstract: Frequency shifts due to radiation fields in the magnetic selection state cesium atom frequency standard,such as the frequency shifts due to Bloch-Siegert effect,microwave spectral impurity,Stark effect,black-body radiation and Majorana transitions,are investigated.The physical causes of these frequency shifts are analyzed in this paper.The magnitudes of the shifts and their uncertainties are evaluated and their effects on the accuracy of the standard are analyzed.In addition,the methods of reducing the shifts and uncertainties are proposed in order to improve the accuracy of the standard.