In order to improve the strain transfer efficiency of the fiber Bragg grating (FBG) sensor for the deformation monitoring of the aerostat airbag skin, the strain transfer characteristics of FBG for the flexible composite skin monitoring were studied. According to the structural characteristics of the flexible composite skin material, a three-layer strain transfer model of "FBG-adhesive layer-skin structure" was established and the strain transfer function was deduced. The strain transfer at each point of the FBG sensor was carried out by analytical and finite element methods. The influence of the relevant parameters of adhesive layer and skin structure on the transmission rate was analyzed and the best packaging parameters of the surface bonded FBG sensing structure were obtained. The research results show that the calculation error of the analytical and numerical methods is less than 5% for the strain transfer efficiency in the middle of the sensor. When the elastic modulus of the adhesive layer is 0.5 GPa, the adhesive length is 40 mm, the adhesive width is 6 mm, and the thickness of the upper and lower adhesive layers are 0.2 mm and 0.1 mm respectively, the strain transfer rate of the fiber grating strain transfer model after packaging parameters optimization can reach 97.04%. It can meet the sensitivity requirements of aerostat airbag deformation monitoring.