With the development of optical fiber technology, it has been widely used in astronomical observation instruments. In astronomical observation instruments, the number of optical fibers usually reaches several thousand. When the spacing of optical fibers is too small, the output spectra is liable to overlap. Without changing the structure, the aliasing spectra is separated by software method, assuming that the intensity distribution of the output spectra is in the form of Gauss function, and the aliasing spectra is separated by Gauss function fitting method. Compared with the output spectrum when the distance between fibers is wider, a better separation effect is obtained. The minimum mean square deviation is 1.43. The results show that this method is feasible in the separation of aliasing spectra.