In order to monitor and diagnose the insulation of high-voltage cable line arresters under running condition effectively, an online monitoring system of cable line arresters based on a wireless measurement network is designed. The system uses zero-flux sensor to measure the leakage current through arrester. With the use of wireless communication and GPS synchronization technique, the voltage reference signal is measured simultaneously. The fundamental resistive current is accurately calculated by the FFT average algorithm. The temperature of MOA varistors is measured by wireless temperature measuring module. In application with RF network and GSM network, field data is transferred to RTU and the master system, which realizes remote data acquisition and real-time data display, data analysis and data management. The field operation shows that the system can meet the high-voltage cable line arresters’ online monitoring requirements.