The invention provides an optical fiber for shaping Gaussian beams into one-dimensional flat-topped beams, provides a method for shaping the Gaussian beams into the one-dimensional flat-topped beams based on the special optical fiber, and belongs to the technical field of laser beam shaping. The fiber core material of the special optical fiber is high-refractive-index SiO2, the fiber core shape can be rectangular, square, hexagonal or octagonal, and the fiber core diagonal distance is 20-800 microns; the fiber core is arranged in a wrapping layer, the material of the wrapping layer is a low-refractive-index molten silicon and the diameter of the wrapping layer is 100-1600 microns; and the wrapping layer is externally provided with a coating layer, the material of the coating layer is nylonor acrylic resin and the diameter of the coating layer is 200-2000 microns. The numerical aperture of the special optical fiber is 0.12 or 0.22 or 0.28. The optical fiber can be spliced with an optical fiber laser output optical fiber so that the Gaussian beams can be homogeneously shaped into the one-dimensional flat-topped beams. The special optical fiber homogeneous shaping method has the advantages of being convenient to use, low in cost, great in shaping effect and convenient to be spliced with the laser output optical fiber without additional mechanism.