When a surface-bonded Fiber Bragg Grating (FBG) sensor is used to measure the strain of a host material, it will effect the strain distribution of the host material. Therefore, this paper explores the relationship between optical fiber strain and host material strain. A theoretical model of strain transfer of the host material to the optical fiber was presented to modify the measured strain, and the interaction between FBG sensor and host material was considered. Finally, the theoretical predictions proposed in this paper were verified by Finite Element Analysis(FEA) and practical experiments. The results show that the error between FEA and theoretical solution is controlled within 5%, and that between theoretical solution and experimental data is controlled within 8%. These mean that the strain transfer mode satisfies the accuracy requirement of surface-bonded FBG sensors. Moreover, the effects of geometrical and material parameters on the average strain transfer rate and the strain transfer rate were analyzed. The obtained results indicate that the average strain transfer rate and the strain transfer rate increase with the Young's modulus of the host material. However, they decrease with increasing the top thickness and bottom thickness of an adhesive layer.