The object of this study is to find out the best shape of the flapping wing's geometry by using Vortex Lattice Method (VLM). With the Micro Aerial Vehicle (MAV) is getting more and more popular; it is needed to use a low cost numerical method during the early stage design. Unlike other numerical methods (such as high-order discontinuous Galerkin method), VLM is a much simpler method. However, it can calculate the flow characteristic fast, and it doesn't require large computer resources. Having these strengths, VLM appears to be a good method for the initial optimization of flapping wing's geometry. In this study, the VLM need to be verified first. By comparing with the result of Bret's work, it is proved that the Fortran code, which based on VLM, is working well to simulate the flow field and calculate the performance parameters, which are Thrust Coefficient (C[subscript, capital T), Lift Coefficient (C[subscript, capital L]), and Efficiency (Eff). This material is shown in chapter Three. Once the validation work is done, this Fortran code can be used on calculating the performance parameters of all kinds of geometry shapes. There are some major variables of geometry, which are Sweep Angle, Taper Ratio, Aspect Ratio, Twist Angle and Dihedral Angle. First, there will be only one variable changed to see the different performance of various geometry. After that, two variables are changed at the same time to find out the best shape of the geometry. This content can be found in chapter four. The result suggest that if there is no angle of attack, the highest efficiency is for backward sweep of 30°, Taper Ratio 0.2 with an efficiency of 0.8914. Once the angle of attack increases, the best shape is with backward sweep of 30°, Taper Ratio of 0.2 with an efficiency of 0.7779. Once its under the high angle of attack status, the best shape is for Aspect Ratio 16 and Twist Angle of -6° with the efficiency of 0.7145.