长期稳定度是评价铷原子频标性能的一项关键指标．物理系统内部静磁场（C场）稳定性引起的磁致频移与铷频标长期稳定度有关．利用⁸⁷Rb原子基态磁敏跃迁频率与轴向外加磁场的线性关系，测量了铷频标物理系统内部磁场强度，并计算了铷频标物理系统磁屏蔽筒轴向磁屏蔽因子约为3 828．实验结果表明磁屏蔽筒有效地降低了地磁场日波动对铷频标物理系统内部C场的影响，使磁致频移控制在合理范围内．

Long-term stability is a key specification for rubidium atomic frequency standards (RAFS), which is influenced by magnetic frequency shift caused by C-field stability. Taking advantage of the linear relationship between the transition frequency of ⁸⁷Rb ground state and external magnetic field, we measured the C-field intensity inside the physical package of RAFS, as well as the magnetic shielding factor of the magnetic shield case. Experimental results indicated that C-field fluctuation inside the physical package could be attenuated by using the magnetic shield case. The axial magnetic shield factor was measured to be about 3 828, which could shield geomagnetic field efficiently and keep the magnetic frequency shift in a proper range.