To realize the one-to-one correspondence between each wavelength and its intensity information based on the original two-dimensional spectrogram measured by an echelle grating spectrometer, it is necessary to obtain a one-dimensional spectral curve from which the optical signal intensity as a function of wavelength can be read directly.The original spectrogram is analyzed and the accurate correspondence between the position of each wavelength spot on the receiving image surface and the detector pixel is obtained to realize the reduction processing of the spectrogram.A polynomial fitting method was used to fit the position coordinates of the wavelength spots on the dispersion direction of the prism and the grating, thus establishing the relationship between the wavelength and the image surface.Experimental results show that the polynomial fitting method can be used to establish a spectrogram reduction model rapidly and accurately, achieving spectrogram reduction accuracy of better than 1 pixel as indicated by the maximum computational error of the model (0.023 92 mm).The proposed algorithm has strong flexibility and universality, making it suitable for calculating the spectrogram reduction model for a variety of echelle grating spectrometer designs.