In response to the real-time monitoring requirements of the aerostat skin deformation， a flexible composite skin deformation sensing method based on fiber Bragg grating （FBG） is proposed. According to the characteristics of the multilayer structure of the skin material and the principle of FBG sensing， a flexible skin sensing structure of "FBG-adhesive layer-base" is designed. Through theoretical analysis of the sensing structure， it is concluded that the average strain transfer efficiency increases with the increasing of the shear modulus of the adhesive layer. In the experiment， two adhesives with different shear modulus， GD414 and DP420， are used to bond the FBG sensor to the surface of the flexible skin and a sensor demodulation experiment system is established. The sensitivity and repeatability of the aerostat flexible composite skin deformed FBG sensor are analyzed. The relationship between the center wavelength of the FBG and the curvature of the FBG encapsulated by two different adhesives is studied. The FBG encapsulated by DP420 adhesive which with larger shear modulus has good linearity and repeatability and its sensitivity can reach 145.4 pm/m-1. Reconstruction analysis of the deformation of the flexible composite skin of the aerostat has verified the feasibility of the sensing method. The research results show that the FBG sensor can be used to monitor the deformation of flexible composite skin and it has broad application prospects in the shape monitoring of aerostat skin.