The optical sensor based on dispersion-turning-point long period fiber grating (DTP-LPFG) modified by graphene oxide (GO) was investigated, and its spectral characteristics and sensitivity to external refractive index (RI) were analyzed. The DTP-LPFG with a period of about 136μm was fabricated by using a quasi-continuous KrF laser in a hydrogen loaded single-mode fiber. GO was fixed on the grating surface by hydrogen bonding to form a GO functionalized DTP-LPFG sensor. The experimental results show that there are a blue-shift and a red-shift of the resonant bands at the lower and higher wavelengths, respectively, and the wavelength separation between the dual peaks increases with the deposition of GO on the surface of the DTP-LPFG. The sensitivity of the resonance bimodal spacing variation of the GO coated DTP-LPFG sensor is about 831.89nm/RIU in the RI range of 1.33~1.38, which is 1.05 times higher than that of the uncoated one.