The evanescent field of fiber Bragg gr ating (FBG) is enhanced with the decrease of the radius of the FBG,which makes it very sensitive to the refractive index change of the ambient medium.However,there is a temperature cross-sensing in the process of measureme nt.For practical applications,it is necessary to solve the temperature cross-sensing problem effectively,and then to improve the measurement range for the refractive index.In this paper,a micro/nano dual-FBG sensor is proposed.The spectral charact eristics of this sensor are analyzed using the fiber core refractive index dispersion equations of the three layers a nd two layers.The simulation results show that the sensitivity to the environmental refractive ind ex increases with the decrease of the FBG radius.Furthemore,we experimentally investigate the refracti ve index sensitivities of the dual-FBG sensor with different radii under tepera ture compensation.The sensitivity of the FBG refractive index sensor with radius of 0.3μm is 1.057μm/RIU.