First of all, By analysising the overheating fault of high voltage switchgear, it is necessary to put forward the of on-line temperature monitoring of the high voltage switchgear. Secondly, the current temperature measurement method is classified and compared, and the design of active wireless temperature measuring system of high voltage switchgear is introduced in detail, including the selection and assembly of hardware, and design of wireless transceiver module and PC software. Finally, performance tests are carried out on the test device after assembly, its performance is good that achieve the purpose of real-time on-line monitoring.