Abstract: In order to get high quality pulse with narrow linewidth, spectral compression of Gaussian pulse was investigated numerically by solving the nonlinear Schrdinger equation. It was found that, when the Gaussian pulse with the central wavelength of 1550nm successively propagated in a single-mode fiber and a photonic crystal fiber, its spectra would be compressed. Further more, when input peak power, pulse width of Gaussian pulse, and nonlinear coefficient of photonic crystal fibers were fixed, there would exist an optimal photonic crystal fiber length. If peak power of the initial light pulse was the greater, nonlinear coefficients of photonic crystal fiber was the larger, the optimal length of photonic crystal fiber was the shorter, the compression ratio of spectra was the greater. The highest spectral compression ratio of 3.47 was achieved for the Gaussian pulse with the input peak power of 110W and the initial pulse width of 0.65ps, while the optimum length of photonic crystal fibers was only 4.152m. The spectral compression of Gaussian pulse was better than super Gaussian pulse under the same simulation condition because of the pulse shape. The results would provide a significant guidance for making the ultrashort pulse fiber laser with narrow linewidth.