Abstract: The southern Tianshan collisional orogenic belt belongs to the middle-southern part of the Tianshan orogenic system in the southern North Asia area between the Siberia and Tarim blocks. It is situated between the Tarim and Kazakhstan-Junggar blocks, and geographically includes the Haerke, Erbin and Hula mountains. The orogen is mainly made up of Paleozoic terranes, which are represented by active continental margins at the southern and northern sides and relic oceanic crusts and accretionary complex (produced during evolution of the Paleozoic southern Tianshan Ocean) at the central region. It is proposed that the southern Tianshan oceanic basin came into being in Sinian through continental rifting, and continued to expand during Cambrian. From Ordovician to Carboniferous, the oceanic basin experienced subduction at both the northern and southern sides, leading to its final closure in late Carboniferous. From Permian to early Triassic, the southern Tianshan orogen experienced the stage of post-orogenic adjustments.