In order to improve the accuracy of the scanning wavelength of the portable grating scanning near infrared spectrometer, on the basis of the dispersion formula of plane diffraction grating and the position & mechanical transmission relationship among the grating, swing rod and screw in the scanning mechanism, a mathematical model of spectrometer wavelength correction is built, and a wavelength correction method is proposed. The method includes three processes. First, the parameters of the wavelength correction model are determined based on particle swarm optimization algorithm. Second, the swing rod length and the correction value of the wavelength are determined based on the swing rod length ratio of the wavelength correction model and full spectrum comparison optimization. Third, the hardware structure adjustment and soft parameter compensation are conducted on the spectrometer. The characteristic wavelength of a standard light source was used to perform wavelength correction experiment on the selfdeveloped portable nearinfrared spectrometer. The experiment results indicate that after wavelength correction the wavelength accuracy of the spectrometer is better than ±1 nm, which satisfies the spectrometer wavelength accuracy requirement, and the results verify the correctness of the spectrometer wavelength error analysis and the effectiveness of the wavelength correction method.