Handheld (portable) ultrasonic flowmeter with external clip-on sensing to measure liquid flow. The installation process is extremely simple, and the all-Chinese man-machine interface makes it easier to operate. The measurement process does not need to destroy the pipeline, do not need to stop production, the sensor does not contact with the measured medium, no pressure loss, and at the same time has the characteristics of battery power, small size, light weight, easy to carry. It can be said that the real sense of mobile measurement flow, online detection.