Outburst floods caused by breaches of landslide dams may cause serious damages and loss of lives in downstream areas; for this reason the study of the dynamic of the process is of particular interest for hazard and risk assessment. In this paper we report a field-scale landslide dam failure experiment conducted in Nantou County, in the central of Taiwan. The seismic signal generated during the dam failure was monitored using a broadband seismometer and the signal was used to study the dam failure process. We used the short-time Fourier transform (STFT) to obtain the time-frequency characteristics of the signal and analyzed the correlation between the power spectrum density (PSD) of the signal and the water level. The results indicate that the seismic signal generated during the process consisted of three components: a low-frequency band (0-1.5 Hz), an intermediate-frequency band (1.5-10 Hz) and a high-frequency band (10-45 Hz). We obtained the characteristics of each frequency band and the variations of the signal in various stages of the landslide dam failure process. We determined the cause for the signal changes in each frequency band and its relationship with the dam failure process. The PSD sediment flux estimation model was used to interpret the causes of variations in the signal energy before the dam failure and the clockwise hysteresis during the failure. Our results show that the seismic signal reflects the physical characteristics of the landslide dam failure process. The method and equipment used in this study may be used to monitor landslide dams and providing early warnings for dam failures.