The necessity and actual application of an on-line temperature monitoring system used for10kV high voltage electric cable of industrial enterprises has been studied in this paper. Selecting method for temperature sensors, composition of temperature monitoring system and its operating have been illustrated as well. The information processing software and trouble shooting expert system software, basic information network of power facility, and on-site bus line technology used in power system are introduced. The online trouble shooting and diagnosis for high voltage electric cable and cable joints with non stop of power supply have been achieved.