Flapping wing micro aerial vehicles (FWMAVs) have attracted more attention during the development of the robotic systems field. The size of the flapping wing plays an important role in the lift force and torque generation based on quasi-steady aerodynamic model. Therefore, it is necessary to study energy-efficient design methods for wings to provide sufficient lift force and torque with minimal energy consumption for hovering flight. In this paper, the sensitive parameters for the lift force and power consumption were first selected based on design of experiment (DOE) and the parameter of the distributed wing stiffness was determined based on experimental data. Design optimization models for three different cases were then built by considering the lift force as one constraint and the energy consumption as the objective function. The combination of subset simulation and the gradient-based optimization was finally used for solving design optimization models, and the corresponding sensitivity analysis was provided.