The spectral characteristics of the single layer optical fiber Bragg grating was analyzed in detail based on single mode effective refractive index of micro-nano optical fiber dispersion equation and the resonance equation of the optical fiber Bragg grating. The single layer optical fiber Bragg grating obtained by FH acid etching.with the decrease of the fiber core radius, the resonance wavelength shift to the lift, and the resonant wavelength numbers are reduced from 5 to 1, until finally disappeared; With the decrease of the refractive index grating external environment at the same time, the cut-off radius reduced, and when the grating external environment refractive index dropped to 1, the cut-off radius reduced to 0.55 μm.