In order to design the driving mechanism of Gurney flaps, we focus on the displacement of the free end of a piezoelectric cantilevered beam. The displacement is derived by Euler-Bernoulli beam model, and a finite element method is used to investigate the influence of the parameters such as the thickness of the substrate and the arrangement position of the piezoelectric sheet on the displacement. The results show that the maximum difference of the displacement predicted by the analytical method and the finite element method is within 3.6%. Reducing the thickness of the substrate, placing the piezoelectric sheet near the root of the cantilever beam and using better materials can obtain relatively larger displacement. The displacement of the piezoelectric cantilevered beam cannot provide enough large displacement to a Gurney flap, so a device to amplify the displacement is necessary.