In this paper, the reflectance of the butterfly wings are measured by using the microspectrophotometer as the optical character with the reflectance on several scales on the wings. Reflectance spectra from different wing scale zones with the same color are dramatically different. And it suggests that the tiny structural difference has the great influence on the reflectance property. In addition, the microstructures of the butterfly wings can be simplified to a 2D crossing grating. By simulating a two-dimensional model using rigorous coupled-wave analysis technique, the optical properties of the butterfly wings were investigated. The simulation results depend strongly on the structural parameters and refractive index. The research will reveal the mechanisms of the structural color of 2D crossing grating butterfly wings.