The invention provides a cluster high-tension switch cabinet online monitoring device and a monitoring method thereof. The cluster high-tension switch cabinet online monitoring device comprises a center integrated console, an Ethernet, a communication converter, a data bus and cluster switch cabinets and is characterized in that each switch cabinet includes an optical fiber temperature sensor, a vacuum breaker optical fiber displacement sensor, a current sensor, a switch cabinet power monitoring module and a data processor, the sensors and the monitoring module transmit data signals to the data processor after collecting the data signals for data analysis and processing, and an ultimate processing result is transmitted to the communication converter through the data bus and then is uploaded to the center integrated console through the Ethernet. By means of the monitoring device and the monitoring method, the operation states of the cluster switch cabinets can be dynamically learnt about in real time, reliability of a power system is improved and maintenance and detection of maintenance staff are facilitated.