Abstract: In view of the shortcomings of the existing transformer temperature measurement technology, the system of surface acoustic wave (SAW)-radio frequency identification (RFID) was proposed for online monitoring of transformer oil temperature. Firstly, SAW tag was designed based on the main structural parameters of interdigital transducer and reflective grating, and SAW tag was calibrated and communication distance tested; Then, SAW-RFID system was used to test the transformer oil temperature of a substation for one year, and the test data was compared with the actual transformer oil temperature data monitored by the temperature sensing probe method. The results show that the temperature error of transformer oil in the two methods is less than 0.8℃. SAW-RFID system can replace the traditional method to realize the online monitoring of transformer oil temperature.