Abstract: The stiffness of flapping wings has a significant impact on the aerodynamic characteristics and structural response of insects in forward flight. Numerous studies have investigatedthe fluid-structure interaction on small insects' flapping wings, while relevant studies on butterflies, particularly those with large and low-aspect-ratio wings, remain limited. Given this, we investigate the effects of different flexible distributions on the fluid-structure interaction characteristics of butterfly-like wings during forward flight. A geometric model and kinematic equations are established based on the real morphology and motion patterns of the Chilasa clytia. Additionally, a fluid-structure interaction solution method based on Lattice Boltzmann Method (LBM) and Finite Element Method (FEM) is developed and validated using benchmark cases. Using the developed method, the aerodynamic characteristics and structural response of isotropic flexible, anisotropic flexible, and rigid butterfly wings have been systematically analyzed. The results show that the isotropic flexible flapping wing exhibits enhanced flight performance compared to the anisotropic wing and rigid flapping wing because it induces more complex vortical structures including the wingtip secondary flow vortex (WSFV) and the hindwing tip vortex (HTV), which result in an additional low-pressure area. This study provides novel insights into the vortex dynamics involving the lift enhancement mechanism in flapping-wing flight and offers valuable guidance for the design and optimization of new bionic flapping-wing MAVs.