An optimal design of a piezoelectric coupled cantilever structure attached by a proof mass subjected to harmonic motions is developed to achieve efficient energy harvesting for applications in high-rise buildings. Energy harvesting is realized from the electromechanical coupling effect by the piezoelectric patch mounted on the cantilever. To describe the energy harvesting process, a mathematical model is developed to calculate the output electrical charge and the voltage from the piezoelectric patch. The corresponding efficiency of the energy harvesting by the piezoelectric coupled vibrating cantilever can then be obtained. The influence of the thickness ratio of the piezoelectric patch to the host beam, the length and location of the piezoelectric patch, the radius of the attached mass, and the excitation frequency of the harmonic motion on the energy harvesting efficiency is investigated for the optimal design. This research provides a new method for absorbing vibration energy of high-rise buildings subjected to harmonic motions such as wind loadings through a design of energy harvesting devices made of piezoelectric coupled cantilever structures.