The strain sensing sensitivity of fiber Bragg grating (FBG) is very high,but it is necessary to solve the temperature cross-sensitive problem effectively in practical applicat ions.Based on the relationship of the core effective refractive index of the FBG and the core radi us,a new type FBG sensor composed of two sections is proposed.An FBG is divided into two sections with e qual length.One of them is eroded using HF acid.So the two sections can be regar ded as two FBGs with different resonant wavelengths.Spectral characteristics of this in-series FBG and analyzed using the dispersion equation of two-layer dielectric fiber and the transfer matrix metho d.The simulation results show that the resonant band is split due to the particularity of the FBG structu re.As the core radius reduces,the resonant wavelength of the etched section of FBG presents a b lue shift,while the resonant wavelength of the other section of FBG remain basi cally unchanged,the distance between two resonant wavelengths is increased with the decrease of the core radius.At the s ame time,strain and temperature are measured,and the sensitivities of strain and temperature sensing are 7.2με and 1.1℃,respectively.