The optical property of the flashing hind wings of the Papilio maackii were measured by an angle resolved spectrum system. A multilayer reflection structure model was established to explain the mechanism of the structural color of the butterfly wings. The circular dichroism in the microstructure of the hind wings of the butterflies was measured and the polarization properties were verified. Based on the structural color, the sensing experiments of the refractive index of solutions by using butterfly wings were designed and implemented. The results show that the spectra of butterfly wings redshift with the increase of the refractive index of solutions. The research provides a technological platform for polarization and sensing applications based on the microstructures in nature.