As the strain transfer theory of existing Fiber Bragg Grating(FBG) sensors does not take its effect on basic material strain into account, this paper researches the strain transfer theory for a FBG sensor bonded on a plate. The strain of an optical fiber is different from that of the plate, so the strain relationship between the optical fiber and the plate was studied to improve the measurement accuracy of FBG sensors. A theoretical model of strain transfer of FBG sensors bonded on the plate was presented, and the interaction between the FBG sensor and the plate was analyzed. Then the theoretical predictions were validated by Finite Element Method(FEM) and experimental data. Finally, the effect of the parameters of the plate on the strain transfer rate was analyzed. The results show that the error between the FEM and theoretical solution has controlled within 4% and that between the FEA and experimental data has controlled within 5%. Moreover, the strain transfer rate increases with the increases of both thickness and Young's modulus of the plate. It concludes that the theoretical model satisfies the accuracy requirement of the FBG sensors, and could provide a design reference for the FBG sensors.