To accurately monitor the strain of surface of host materials, taking the surface fiber Bragg grating (FBG) sensor as an example, the relationship between the strain measured by the surface FBG sensor and the actual strain of the host material is deduced. The general expression of strain transfer coefficient of the surface FBG sensor is got. In experiment, the copper slice packaged FBG sensor by is adhered to the cylindrical sample surface and its strain transfer coefficient is got. The experimental result proves that the difference between strain transfer coefficients obtained in theory and in experiment is small and the theoretical derivation of the strain transfer coefficient is rational. The research results provide the theory guidance for the FBG sensor packaging and application.