Abstract: The study of unsteady flow mechanism and aerodynamics performance of flapping wing is very significant for micro aerial vehicle (MAV) design. In this paper, hybrid dynamic mesh technique and unsteady flow solver are used to study the flapping motion of a seagull wing. Radius basis function (RBF) interpolation approach is adopted to generate the moving mesh. The reduced selection of surface reference points is used to save the time consuming of the RBF interpolation. In order to satisfy the geometric conservation law on the moving mesh, the normal velocity of cell interface is calculated by its 'sweeping volume'. A 3D model of seagull wing is built based on observation data and a simple flapping, and the folding motion is also modeled. Influence of the flapping angle, the folding angle and the folding phase is analyzed. Numerical results show that the folding mechanism can weaken the disadvantage of the upstroke. Therefore, with an increasing folding angle, the averaged lift coefficient increases and both the drag and power consumption decrease. Furthermore, increasing the proportion of folding process and decreasing the unfolding process are helpful to improve the time-averaged aerodynamic performance and reduce the power consuming.