The Ganzi- Litang ophiolite mélange belt is located in the eastern section of the ‘Three- River’ archipelagic arc basin system in southwest China. Geologists have paid close attention to this region with a view to study the development and evolution of the paleo- Tethys ocean. This study conducted detailed research on the rock assemblages and sedimentary characteristics of the ocean island rock association from the Xinlong- Litang area in the middle part of the Ganzi- Litang Ophiolite Mélange Belt. The different types of oceanic island rock assemblages in the study area are divided into the Cunge Formation with platform facies, the Dasenlongwa Formation with slope facies, and the Adalong Formation with slope foot facies. Isotope chronology and paleontological studies show that the formation age of the oceanic island- type rock assemblages in the study area extends from the Early Permian to the Late Triassic, suggesting that the Ganzi- Litang ocean basin existed as a mature ocean in the Early Permian, and the volcanic activity continued into the late Triassic. Based on the distribution characteristics of different types of oceanic island rock assemblages and differences in metamorphic deformation, it is inferred that the oceanic island debris found in the Xinlong- Litang area in the middle part of the Ganzi- Litang ophiolite melange belt could not belong to a single ancient oceanic island, but is the debris after subduction and emplacement of different ancient oceanic islands at different times. The results achieved by the authors have significantly advanced the study of the evolution of the Ganzi- Litang ophiolite mélange belt by providing new data and evidence for the accurate understanding of the tectonic evolution process in the Ganzi- Litang oceanic basin.