A free standing 2D PS colloidal crystal with Au nanoshells/hydrogel composite film (CAuHCF) was fabricated by embedding a 2D PS colloidal crystal with Au nanoshells into a polyacrylic acid (PAA) hydrogel film. This CAuHCF can act as a visualized sensor with high diffraction intensity. The 2D PS colloidal crystal with Au nanoshells was prepared by depositing an Au layer on PS colloidal crystal obtained by interfacial self-assembly. The diffraction intensity of the CAuHCF was increased by about 30-fold than that of traditional 2D PS colloidal crystal/hydrogel composite film on transparent substrate due to large scattering cross section of Au shell. Such sensors based Au nanoshells array with the simple preparation process and the strong diffraction signal are promising ones for practical applications in visual detection. Additionally, with the simple preparation process and high diffraction intensity, other visualized sensors based different hydrogel matrix and the 2D PS colloidal crystal with Au nanoshells could be synthesized for monitoring various analysts.