Abstract: In order to calibrate deviations of demodulation system between rising slope and falling slope of triangular wave on demodulation results of FBG waves, effective calibration method of relative position to sampling point is proposed. Two FBG waves in two scanning process of triangle wave are mapped to the corresponding original data of etalon spectrum firstly. Then positional deviation of two FBG waves which is mapped into the etalon spectrum is corrected. In this way demodulation deviation of system can be reduced. Two FBGs with different wavelength to accomplish.in experiments. Results show that the wavelength deviation of FBG1 is reduced from 12.053 pm to 0.476 pm, while wavelength deviation of FBG2 is reduced from 12.101 pm to 0.427 pm. Demodulation deviations of two FBGs are decreased respectively by 25.3 times and 28.3 times than before.