Abstract <p>To achieve rapid calculation of the aerodynamic forces of multi-wing butterfly-inspired ornithopters during flight, a quasi-steady aerodynamic force calculation method driven by multiple parameters and based on the blade element theory (BET) is proposed. This quasi-steady method can describe the flapping motion, the wing shape and the deformation rules of each wing, whether observed or expected, and calculate the instantaneous aerodynamic forces of the ornithopter according to the incoming flow conditions. The motion phase differences of each wing in the multi-wing ornithopter are also taken into account. Compared with the aerodynamic force measurement experiment of a 200-mm wingspan butterfly-inspired ornithopter, and considering the influence of the wing moment of inertia on the experimental measurement, the results show that the instantaneous values of the lift and thrust forces are consistent, and the maximum normalized peak error of the instantaneous lift force is 7.2%, and that of the instantaneous thrust force is 5.7%. This method can effectively describe changes in the aerodynamic force during the flight of butterfly-inspired ornithopters and provide guidance in the preliminary design stage.</p>