The external clamp-on ultrasonic flowmeter is a flow meter that is highly suitable for full pipe measurement in pipelines. It features easy installation, non-contact operation, and can measure the flow of large-diameter media as well as media that are difficult to contact and observe. Its measurement accuracy is very high and is almost unaffected by various parameters of the measured medium. It can especially solve the flow measurement problems of highly corrosive, non-conductive, radioactive and flammable and explosive media that other instruments cannot handle.