The Tianshan Mountains are a huge intracratonic orogienic belt, lying in Central Asia. It underwent polygenetic metamorphism and deformation in the Paleozoic. Therefore the Tianshan orogeny is regarded as a representative of the Hercynian orogeny in China.The Central Tianshan Mountains were formed in the Early Palaeozoic and later experienced intense reconstruction. Recently the authors have obtained several 40Ar/39Ar cooling ages and other isotopic ages of this area. On the basis of these ages combined with previous age data and in comparison with the regional stratigraphic contact relationships, the Central Tianshan orogeny is divided into five stages, whose isotopic ages are about 315 - 289 Ma, 327 - 334 Ma, 345 - 355 Ma, 402 - 412 Ma, and 439 - 452 Ma respectively. The Mesozoic Era might have witnessed three tectonothermal events with isotopic ages of about 226 - 200 Ma, 165 -160 Ma and 83 Ma, representing the later evolution of the Central Tianshan Mountains.Most of the above-mentioned ages were obtained by dating the tectonites from the fault zone at the southern margin of the Central Tianshan Moutnains. Their coincidence with regional ages indicates that the overthrusting along two boundary faults of the Central Tianshan Mountains might be the fundamental mode and cause of the deformation of the Central Tianshan erogenic belt.