Based on the localized surface plasmon resonance (LSPR) effect of the large-sized gold nanoshells (AuNS),the principle and characteristics of fiber Bragg grating (FBG) LSPR refractive index (RI) sensor was studied.The physical mechanism of the RI sensitivity enhancement of the AuNS for the sensor was studied by the finite difference time domain method.The LSPR RI sensor based on the etched fiber Bragg grating (eFBG) was constructed,and the response spectra under different surrounding refractive index (SRI) environments were obtained.The experimental results show that the intensity-based RI sensitivity of the eFBG-LSPR sensor was －72.33 dB/RIU,which was 61.3 times higher than that of eFBG,verifying the validation of the theoretical analysis.The proposed sensor has good application prospects in the fields of biochemical sensing and environmental monitoring.