The continental crust covers 40% of the Earths surface area, and its genesis and growth is fundamental to maintain life and supply resources to our society. Growth of the continental crust is commonly ascribed to tectonic accretion of island arc and underplating of mantle- derived magmas, but lacks in the period of continental collision. The Tibet Plateau has the thickest crust on Earth, and thus it is the most outstanding natural laboratory for studying formation, growth, thickening, evolution and preservation of the continental crust. Together with the published data, we found that the emplacement and underplating of the mantle- derived mafic magmas (270~66 Ma) induced by subduction of the Paleo- and Neo- Tethys oceanic slab resulted in horizontal accretion and vertical growth of the continental crust and contributed to 10 km of crustal thickening. In the period of syn- collisional stage (65~41 Ma), Paleocene- Eocene mantle- derived magmatisms were triggered by rollback and breakoff of the subducted Neo- Tethyan oceanic slab during Indo- Asian collision, which resulted in the formation of juvenile crust and 6~9 km vertical growth of continental crust in the Gangdese belt. In the period of late- collisional stage (40~26 Ma), 10~20 km of crustal thickening can be attributed to tectonic thickening due to intracontinental thrusting, while partial melting of lithospheric mantle induced by upwelling of asthenosphere along the mantle- flow channel produces basaltic rocks and lamprophyres which emplaced in the hinterland of the Tibet Plateau. In the post- collisional stage (25~0 Ma), crustal extension has contributed little to crustal thinning both in the collisional front and in the hinterland, accompanying with emplacement of small- volume juvenile mantle- derived magmas and strong denudation. Our results indicate that the proportion of juvenile crust generated and preserved in collisional orogens exceeds 28% of the whole crust in the Tibet Plateau, while 75% and 25% of these juvenile crustal materials were associated with oceanic subduction and continental collision, respectively. We propose that the formation of the thickest crust on Earth can be attributed to both addition of mantle- derived magmas into the crust and tectonic shortening of the middle- lower crust. Thus, formation of the thickened Tibet crust is characterized by growth of juvenile crust and reworking of ancient crust. The thickened Tibet continental crust has an andesitic bulk composition, which could be mainly resulted from intensive remelting of mafic juvenile lower crust and volumious emplacement of felsic magmas.