Abstract: There exists a considerable amount of water in standing trees. The moisture content of standing trees is of great significance to the disciplines of plant physiology, the wood drying, plant irrigation, quality evaluation of trees and prevention of disease and pest. One of the methods for the determination of standing trees is lateral impact vibration. The moisture content can be determined by measuring the resonance frequency of standing trees. The traditional tool used to induce the vibration is the wood hammer. However, it relies on human and can’t induce constant excitation. In view of the above limitations, an automatic excitation device is developed. The device consists of two parts, the mechanical structure and the control system. The mechanical structure includes the stepper motor, the mechanical arm and the base. The control system includes the MCU, the remote controller, the wireless receiver, the LCD and the stepper motor driver. The operation mode of the device can be set by the keys on the MCU or the remote controller. The device strikes the standing tree laterally and induces the vibration. It produces stable force, works automatically and promotes the efficiency remarkably in practical application.