采用耦合模微扰理论推导了旋转磁光布拉格光纤光栅（MFBG）的耦合模方程，利用打靶法数值分析了旋转导致的折射率变化对光栅光谱旁峰的影响，得到了与文献一致的结果。提出“磁圆相关损耗”的概念，并用于分析旋转磁光光纤光栅的磁场敏感性。研究表明，高速旋转（或各向同性）MFBG的磁圆相关损耗特性具有最佳的磁场敏感性；而适当低速旋转的MFBG可获得更高的磁圆相关损耗峰值，有助于提高光栅磁场敏感性的测量精度。与“偏振相关损耗”方法相比，“磁圆相关损耗”方法对线双折射的依赖性更小，理论分析也更简便。

According to the coupled-mode perturbation theory, the coupled-mode equations for spun magnetically-induced fiber Bragg gratings (SMFBG) is derived. The dependency of grating spectra on the spun-induced refractive index change is numerically analyzed by using the shooting method and the theoretical results are identical with the experimental data from literatures. The concept of magnetically-induced circular-polarization dependent loss (MCDL) is proposed for analyzing the magnetic field sensitivity of SMFBG. It is shown that the MCDL of high-speed spun (or isotropic) SMFBG possesses optimal magnetic field sensitivity; however, the appropriately low-speed spun MFBG has a larger peak MCDL, which is helpful to magnetic measurement. Compared with the polarization-dependent loss (PDL) method, the MCDL method is less dependent on linear birefringence and is more convenient for theoretical analyses.