The invention discloses a self-assembly of a brush-shaped block polymer containing PEG segments as well as a synthesis method and application of the self-assembly. According to the self-assembly material, the PEG is introduced into the brush-shaped block polymer, and the one-dimensional photonic crystal with bright structural color is prepared through melting self-assembly and cooling limited crystallization, so that the refractive index difference of two sections of the brush-shaped block polymer is effectively improved, the preparation process of the one-dimensional photonic crystal is simplified to a great extent, and the long-wavelength one-dimensional photonic crystal is prepared under the condition that the polymerization degree of a main chain is small. In the process of preparing the one-dimensional photonic crystal, through melting self-assembly and cooling limited crystallization, compared with solvent evaporation self-assembly, the controllability is higher, and the method is easy and convenient to operate, fast to assemble and low in cost. The prepared one-dimensional photonic crystal has good temperature response, thermal repair, pattern splicing and other properties,and has huge application prospects in the aspects of information counterfeiting prevention, thermal sensing, melt spinning, 3D printing, silk-screen printing, functional coatings, optical fibers and the like.