In order to detect the overheating fault of high-voltage switch contacts in time, and enhance the reliability of power supply system, this paper presents a new method for temperature rise monitoring, it is realized by WSN (wireless sensor network) and electromagnetic coupling which is a power-gaining technology. Based on the above method and technology, the author designs an on-line system to monitor the temperature rise of high-voltage switch contacts and builds a WSN based on ZigBee protocol. The system includes integral temperature collectors and data receiver, and the data between two of them is transmitted wirelessly by using the opening frequency band of 2.4 G provided by wireless module. The integral temperature collector does not need external power for its power is provided directly from high-voltage bus by the principle of electromagnetic coupling. The extensive system tests show the measurement error of temperature is ± 1.5°C, which can meet the temperature measurement requirements of high-voltage switch contacts.