Abstract: Central air-conditioning water system testing is an indispensable testing item in building energy-saving testing. Ultrasonic flowmeter is a commonly used testing method of air-conditioning water system. But its test results are easily affected by the preparation work before testing, sensor installation position, installation method and other factors. Therefore, it is of great significance to summarize the common problems in testing of air conditioning water system by the ultrasonic flowmeter, then to obtain accurate test results. Based on years of working experience in building energy-saving testing and specific cases, the paper elaborates on the issues that should be paid attention to when using ultrasonic flowmeters in the testing process, and provides references for related testing cases.