Under harsh environment with high voltage and intensive electromagnet field, a specific design of a wireless temperature monitoring system is presented in the paper. In High-Voltage Switchgears application, a temperature interrogation device is placed in the high voltage end, and a monitoring instrument is applied in low voltage end. The voltage isolation issue is solved by RF transmission strategy. Moreover, the whole system is optimized for low-power application, with single battery supply and up to 10 years service life. The wireless interrogation device, which is at the High-Voltage (HV) Circuit Breakers Contacts and is based on wireless transmission technology, realizes the functions such as the interrogation of contacts temperature, real-time alarming and signal processing. The RS-485 interface connects the temperature monitoring instrument and the host computer. It makes it flexible to expand the system.