Abstract: Online flow monitoring (OFM) data provides fundamental support for flood and drought disaster prevention, water resource management and water ecological environment protection in river basins. This paper summarizes the advantages and disadvantages of main international OFM technologies, based on a comprehensive review of their current status in China and abroad. Taking Changjiang River Basin as a case study, the OFM performance of typical stations is evaluated from three perspectives: overall performance, different contact configurations, and different river types, with systematic error and random uncertainty as evaluation indicators. The results show that the OFM technologies and devices have been effectively applied in the Changjiang River Basin, with a coverage rate of 43.6% for hydrological stations. A few stations achieve a systematic error within 1% and a random uncertainty within 10%. Contact-type devices perform better than non-contact ones, and the performance of various monitoring technologies is superior in large rivers compared to that in medium and small rivers. There remains significant potential for improvement in the accuracy, universality, and stability of OFM due to the comprehensive influence of environmental conditions, technology, and artificial error. The findings of this study can serve as a reference for the construction of national water networks, digital twin basins, and hydrological modernization planning, thereby supporting high-quality development in the new phase of water conservancy.