Abstract: The boundary between Gondwanaland and Pan-Cathaysia mainland has not yet come to a consensus, which restricts the understanding of the tectonic patterns of Tibetan Plateau and Sanjiang Orogenic Belt, and the evolution of the Tethys Ocean.On the basis of sorting out different viewpoints, combined with new geological survey data and research results, the geological characteristics, development time limit and tectonic setting of ophiolitic mélange in different periods in the Longmu Co-Shuanghu suture zone and Changning-Menglian suture zone were systematically summarized.The Longmu Co-Shuanghu and Changning-Menglian ocean basins have experienced similar processes of ocean basin expansion, subduction and arc-arc (continent) collision orogeniy, and basically have the same deep subduction and orogenic time, indicating that they have affinity in tectonic attributes.It is believed that Longmu Co-Shuanghu-Changning-Menglian Tethys oceans together constitute the remnants of the Proto-Paleo Tethys Ocean after its final extinction.The basement of the south and north Qiangtang blocks have different aeromagnetic anomalies on both sides of the Longmu Co-Shuanghu Tethys Ocean, indicating that the evolution process of the blocks is different.Bounded by the Longmu Co-Shuanghu-Changning-Menglian Tethys oceans, the south block is Mesozoic Gangdese-Himalayan orogenic system on the northern margin of Gondwanaland, and the north block is Late Paleozoic Qiangtang-Sanjiang orogenic system on the southern margin of Pan-Cathaysia mainland.The two orogenic systems have undergone different tectonic evolution processes.Combined with other regional data such as biota and geophysics, it is suggested that the Longmu Co-Shuanghu-Changning-Menglian suture zone is the boundary between Gondwanaland and Pan-Cathaysia mainland in the Tibetan Plateau.