Because the vibration of buildings and bridges is often small in amplitude, low in frequency, and wide in frequency bandwidth, designing a conventional energy harvester with the natural frequency low enough to coincide with the low excitation usually accompany with very large mass and volume. However, it is very important to use portable energy harvester (usually with higher natural frequency) to obtain energy for wireless devices. If portable energy harvesters were used directly on high-rise buildings, the efficiency would be very low. To solve this problem, we propose a simple device to implement portable energy harvester in high-rise building application environment with a high efficiency. It is an intermediate spring-mass system to be installed between the energy harvester and the underlying building. The crux of this device is to enhance the vibration amplitude of the oscillating mass of energy harvesters, so that more energy can be harvested. By changing the degree of freedom (DOF) and stiffness of the intermediate device, the performance of energy harvester can be drastically enhanced. The effects of the parameters of the device for the harvesting performance have been identified using the Lyapunov method, and the conclusion has been verified using four earthquake ground motions. Applications to 100-story buildings are used to demonstrate the efficiency of the proposed intermediate device. In the illustrative examples, this device can increase the generated energy of linear electromagnetic energy harvester (EMEH) up by several hundred times.