Abstract: To better study the acoustic field characteristics of focused ultrasound transducers, this paper proposes a method for measuring the focal region size using infrared thermal imaging technology. By placing a thin-film sound-absorbing material on the focal plane of the transducer and measuring the temperature distribution under ultrasonic power using an infrared thermal imager, the focal size is determined. Additionally, the hydrophone scanning method was used to measure the same focused transducer, and a theoretical analysis of the sound field distribution was conducted. The results showed that the discrepancy in the -6 dB beam width was within 5%, verifying the feasibility of using infrared thermal imaging to measure the sound field distribution of focused ultrasound transducers.