The invention provides a system for on-line monitoring abnormal vibration of a GIS equipment isolating switch. The system comprises a signal acquisition unit formed by a piezoelectric type accelerometer and a current transformer, an equipment terminal signal processing unit formed by a filtering amplification module, a high-speed AD sampling module, a DSP module, an ARM processor module, a communication module and a power supply module, a sensor disconnecting-prevention unit formed by a connection board, a connecting fixing member, a copper sheet, a controller and a piezoelectric transducer, a background monitoring server and a human-machine interface. During use, the signal acquisition unit acquires vibration and current signals and sends the vibration and current signals to the equipment terminal signal processing unit for processing, the equipment terminal signal processing unit sends preprocessed information to the background monitoring server for monitoring and determining, and the sensor disconnecting-prevention unit assists in fixing the piezoelectric type accelerometer and gives off an alarm when the piezoelectric type accelerometer falls off. The system has the advantages of simple structure and easy realization and ensures timely fault discovering, rapid response and highly-reliable operation during use.