The invention discloses a portable test device for the natural vibration characteristics of a transmission tower. A real-time dynamic data collection module, a wireless signal transmission device and a lithium battery are installed in a test box. A laptop and a wireless signal receiving device are arranged in a workstation set on the ground, and a dynamic signal analysis system is pre-installed in the laptop. A two-direction accelerometer and the test box are fixed on an upper pole of the transmission tower. The real-time dynamic data collection module in the test box collects an acceleration signal in the two-direction accelerometer. The acceleration signal is transmitted through the wireless signal transmission device, and the wireless signal receiving device in the workstation receives the acceleration signal. The dynamic signal analysis system in the laptop processes the acceleration signal and obtains the natural vibration frequency and structural damping of the transmission tower in two directions in real time. The test device has the advantages of light weight, quick installation, no need of wiring and no need of 220V power supply. Only one set of the device can quickly and easily test the vibration frequency and damping of multiple transmission towers in the field.