A segregated model for strain transfer coupling in a surface-bonded fiber Bragg grating (FBG), adhesive, and measured object was established. In addition, the correction relationship between the FBG-measured and true strains on the surface was derived. The theoretical values were verified by finite element simulation and experimental results. Its accuracy and viability under various installation conditions were also discussed. The theoretical results match the experimental results well, with errors below 1.6%. The strain sensing coefficient and its accuracy are positively correlated with the adhesive length and elastic modulus of the protective recoating, while they are negatively correlated with the mechanical strength of the measured object. In addition, the accuracy of theoretical strain sensing coefficient is negatively correlated with geometrical features of protective recoating and adhesive, with an insensitive strain sensing coefficient. This study provides reference for strain measurements using a surface-bonded FBG, error correction, and design of relevant sensors.