The invention discloses a rock soil body instability hazard monitor and warning method based on external excitation and a wavelet packet energy spectrum, and belongs to the technical field of geotechnical engineering monitoring. According to the rock soil body instability hazard monitor and warning method based on external excitation and the wavelet packet energy spectrum, stability zoning is conducted based on the mass grade of a rock soil body, and a rock soil body stability monitoring point is chosen; a three-axis acceleration sensor is distributed in the rock soil body stability monitoringpoint; external excitation is applied by adopting a construction (production) blasting or percussion excitation mode, and shock wave response signals of external excitation are collected through thethree-axis acceleration sensor; wavelet packet decomposition is conducted on the shock wave response signals of external excitation, and the wavelet packet frequency band energy ratio of three directions of the three-axis acceleration sensor is calculated correspondingly; and instability warning indicators namely energy ratio accumulation variant P of all monitoring points in all directions is calculated and monitored, variation tendency is analyzed, and the rock soil body stability is evaluated and pre-warned.