Through the model of cascading retarder and rotator, the polarization transmission characteristics of birefringent fiber in magnetic field have been studied. By multiplying their Jones Matrixes in different cascading order, we have deduced the analytic expressions for the phase shift and fast axis orientation of the equivalent retarder as well as the angular rotation of the equivalent rotator. When linear birefringence and circular birefringence occur in the same fiber, it is found that the equivalent phase retardation in unit length is not equal to its inherent birefringence, nor the equivalent angular rotation is equal to its Faraday rotation. They are relevant meanwhile both to the inherent linear birefringence of fiber and to the circular birefringence caused by the magnetic field. What’s more, in the equivalent models with different cascading order, the fast axis of the equivalent retarder does not coincide with the linear birefringent axis of fiber, but has an offset angle respectively with opposite spin-wise, and the offset is just equal to the half of the equivalent angular rotation.