In order to eliminate the fiber Bragg grating demodulation error caused by the interference peak shifting of Fabry-Perot etalon, a method was proposed that multi-gratings were utilized to calibrate the wavelength of Fabry-Perot etalon, and a demodulation platform was established. Sampling channels were respectively connected with sensor gratings, Fabry-Perot etalon and reference gratings, and interference peak wavelengths with high precision were calibrated using multi-reference-gratings. Then wavelengths of sensor gratings were calculated using these wavelengths, and calibration error was reduced. The experiment demonstrates that the repeatability error of the fiber Bragg grating demodulation system is less than 1.6 pm, and the wavelength demodulated error is under than 1.8 pm.