The invention relates to a rock slope instability pre-warning system and method under an excavation disturbance condition and belongs to the field of great geotechnical engineering. The pre-warning system comprises a micro-shaking monitoring system, a network transmission system, a numerical calculation analysis system, a virtual reality system and a pre-warning forecast analysis system. The micro-shaking monitoring system can effectively catch the time, the space time and the energy of a fracture micro-shaking event in slope rock. The network transmission system is used for transmitting the monitored micro-shaking data to the pre-warning forecast analysis system. The numerical calculation analysis system considers the slope rock damage caused by micro-shaking and achieves calculation analysis on slope deformation evolution and stress migration. The virtual reality system is used for visually and directly displaying the formation, evolution and development process of slope instability and provides a basis for reasonable reinforcing and supporting. The pre-warning forecast analysis system achieves dynamic and real-time pre-warning for rock slope instability under excavation disturbance according to deformation acceleration, stress field migration and micro-fracture evolution characters.