The performance and lifespan of composite materials used in aviation, automotive, manufacturing, and other fields are seriously affected by the occurrence of delamination damage and internal micro-cracks. A novel, effective, and large-area monitoring method is urgently needed to monitor the structural health of such materials. In this study, the deformation monitoring of composite materials is realized by analyzing the transverse stress-induced linear birefringence of single-mode fiber, based on the principle of distributed optical frequency domain reflection (OFDR) and polarization analysis technology. First, the relationship between the transverse stress and bending radius of fiber embedded in composite material is analyzed using ANSYS. Then, by measuring the linear birefringence of a single-mode fiber with a cladding diameter of 250 μm or 165 μm under different bending radii, we obtain the empirical expressions of linear birefringence and bending radius. The results are in concordance with the change trend demonstrated via simulation. A greater bending deformation implies a greater fiber linear birefringence. The proposed method points to a new direction for the effective and convenient monitoring the structural health of composite materials, and it possesses significance in the field of structural damage monitoring.