ABSTRACT A computational fluid-structure interaction (FSI) model for simulating passive motions in flexible insect wing flapping in air was developed. The model wing reduces the complicated network of veins to a few narrow supporting areas in the shell finite elements based on the macroscopic constitutive relationships, and it was used in a three-dimensional FSI finite element analysis, where a monolithic equation system for the FSI was efficiently solved using a projection method. Data for actual insects were incorporated to the FSI model with the aid of the FSI dynamic similarity law. A flapping motion was imposed on the model wing base, while any other wing’s motion was created as the result of the FSI induced by the flapping motion. The simulated feathering and cambering motions were very close to those for actual insects. The results demonstrate the ability of the FSI model to quantitatively evaluate the actual physics of flapping insect wings. The proposed model is expected to lead to new design concepts based on the constructive use of the FSI in the development of insect-inspired flapping-wing air vehicles.