The Tianshan orogen underwent longlived subduction/accretionary orogenesis and complicated intracontinental reactivation since Neoproterozoic, it is a typical composite orogenic belt. Based on the recent research progress, this article analyzes available structural, metamorphic and chronological data of the Precambrian basement, Paleozoic sedimentary sequences, arctype magmatic rocks in the Yili, Central Tianshan and South Tianshan units, as well as the deformed and metamorphic rocks along the major suture zones, and summarizes geological records for three major transitional tectonic events. ① The first transitional event from passive to active margins is suggested by the Middle to Late Ordovician continental arc magmatism and changes of sedimentary environments in northern and southern Yili block, Central Tianshan and northern Tarim. ② The second transitional event from advancing (Eastern Pacifictype) to retreating (Western Pacifictype) subduction regimes is proposed on the basis of Late Silurian to Early Devonian intensive ductile deformation and amphibolite facies metamorphism recorded in the Early Paleozoic rocks of the Yili and Central Tianshan blocks, this event was also a response to the amalgamation of the Kazakhstan microcontinent; subsequently, continental arc magmatism under extensional setting related to retreating subduction regime occurred in the Yili and Central Tianshan blocks during Late Devonican to Carboniferous, and a series of backarc limited oceanic basins formed simultaneously in South Tianshan. ③ The third transitional event from convergent orogeny to postorogenic intracontinental tectonics is evidenced by widely developed late Carboniferous thrusting and Permian strikeslip shearing, latest Carboniferous to Early Permian olistostrome, and Early Permian postcollisional magmatism. Deciphering these transitional tectonic events is critical in understanding the orogenic processes and geodynamics of the oceanic basins within the PaleoAsian Ocean from subduction initiation, switching of subduction regimes and subduction termination.