In view of the fact that the spectrum recovered by the nonlinear optical path difference will appear additional frequency noise, which will lead to the broadening of the restored spectral line and seriously affect the spectral quality, a method for interferogram nonlinear optical path difference correction and wavelength calibration is proposed by measuring the characteristic light source only once. By single measurement of the characteristic light source, the interferogram can be obtained, the nonlinear phase and approximate central frequency contained in the interferogram can be calculated, and the relative optical path difference can be calculated. Then, the nonlinear mapping relationship between the optical path difference and the sampling point can be obtained. Finally, the nonlinear optical path difference can be corrected by the secondary sampling. Taking the static birefringence Fourier transform spectrometer as an example, the nonlinear optical path difference model of the system is constructed, and the correction method and principle of nonlinear optical path difference are given. Then, the mercury argon lamp is used as the characteristic light source, the characteristic spectral lines of mercury argon lamp are extracted by the obtained interferogram, and the influence of different wavelengths on the nonlinear optical path difference is analyzed. Finally, the nonlinear optical path difference is corrected and wavelength is calibrated. The experimental results show that the half-peak full width of the spectral line at 546.074 nm changes from uncorrected 9.08 nm to 4.14 nm, indicating that the proposed method effectively improves the resolution and accuracy of the spectrometer.