In recent years, wireless power transmission systems have gained widespread recognition compared to traditional charging systems due to their convenience, safety, and environmental friendliness during usage. However, the problem of unstable receiving voltage caused by coil misalignment during wireless charging severely hinders the extensive application of this technology. To address this issue, this paper proposes a method to optimize the controller using a proportional-integral (PI) strategy. The optimized controller is employed to steady the secondary-side circuit after coil movement, maintaining a stable charging voltage. To validate the effectiveness of the proposed method, simulation experiments and hardware tests are conducted in this study, comparing it with other optimization algorithms. Experimental results and figures demonstrate that the controller optimized with proportional-integral strategy can more effectively control the stability of the load voltage.