Structure optimization is an overall plan method that balances structure weight, structure strength and material distribution to the greatest extent. In this document, we firstly execute topological optimization method on a usual aircraft’s flap crank to acquired the primary form of structure based upon Altair Optistruct, then use size optimization method to obtain the approximate size of crank, and lastly get an optimal crank by considering strength, stiffness, technics and utilization of material.