Background <p>Dragonfly wings exhibit exceptional aerodynamic performance, largely due to their passive inertial deformations during flapping, which are crucial for lift generation and attitude control. Understanding and replicating these deformations is key to advancing the design of flapping-wing micro air vehicles (FWMAVs). However, directly measuring the inertial deformations of natural wings in situ remains a challenge.</p> Objective <p>This study aims to characterize the full-field inertial deformations of entire dragonfly wings while preserving their natural constraints and posture.</p> Method <p>Here we present a novel method combining base excitation with common-path electronic speckle pattern interferometry. By exciting the wing base at its first two natural frequencies, we isolate and amplify the inertial bending and torsional deformations.</p> Results <p>Our results reveal that the torsional axis of the wing is coincident with the crest line of its bending deformation. Furthermore, by correlating higher-order mode shapes with the venation architecture, we find that the forewing functions analogously to a 'sail with a spar', whereas the hindwing resembles a sector of an 'umbrella'. This tandem configuration with distinct mechanical roles likely underpins the dragonfly's superior maneuverability.</p> Conclusions <p>The proposed method has achieves the measurement of the inertial deformation of the dragonfly wings<b>.</b> The findings provide quantitative insights into the passive deformation mechanisms of dragonfly wings and offer a bio-inspired design rationale for the next generation of high-performance FWMAVs.</p>