Abstract: There are Mesozoic intrusive rocks along the Lancang River in Chala area of eastern Tibet, which mainly occur as complex batholiths and apophyses and lenticular granite that intruded in Early Carboniferous Kagongyanka Formation and Jitang Group metamorphic rocks. The intrusive rocks are mainly composed of monzonitic granite and granodiorite with a little diorite. So far, the genesis of these rocks, including their formation age and tectonic significance, has been poorly studied. In this paper, four granite samples were used for LA-ICP-MS U-Pb dating, and the dating results show that the age of a sample is 219.8Ma±2.4Ma, and the ages of the other three samples are 239.2 Ma±1.7 Ma，241.5 Ma±2.3Ma and 242.5 Ma±1.6Ma respectively, suggesting similar formation ages in Middle- Late Triassic period. Geochemical studies indicate that these granites were formed in intraplate syncollisional to post-collisional tectonic setting which underwent the evolution from early collision to the last stage of orogeny. The environment was a tectonic regime of the transformation stage regarded as a “post-orogenic” tectonic environment which was produced by crust anatectic melting as a result of crust extension and rapid uplift after the collision between the eastward Lancangjiang plate and the Changdu micro-plate.