Based on special working condition of high voltage cable insulation layer aging easily and power cable insulation failure， which affected normal production， online insulation real-time monitoring system of underground 10 KV power cable was analyzed in this paper. Hardware and software development were completed through judgment of cable insulation made by ac superimposition method. According to field simulated experiments， cable insulation online monitoring system had good accuracy and sensibility， which provided reference value to other cable insulation monitoring.
