Ultrasonic flowmeter is a non-contact instrument, which can not only measure the medium flow of large pipe diameter, but also measure the medium that is not easy to contact and observe. Its measurement accuracy is very high. The external clip installation can reach the highest accuracy of ± 0.5%, and it is almost free from the interference of various parameters of the measured medium. In particular, it can solve the flow measurement problems of highly corrosive, non-conductive, radioactive, flammable and explosive media that other instruments cannot.