Abstract: In this paper the Sanjiang tectonic belt in eastern Tibet is dividedinto three continental blocks （which are the Zayu block, Qamdo-Simao block and Zongza block from west to east）and two junction zones （the Bitu-Changning and Menglian juntion zone and the Jinsha River-Ailao Mountains junction zone） and a systematic exposion is made about the geological and structural features of various tectonic units and the evolutionary stages of the tectonic belt. The basic features of the evolution of the belt are as follows: during the Late Permian the Bitu oceanic basin was subducted eastward and the Jinsha River back-arc basin was subducted beneath the Qamdo block; in the Early Triassic the Jinsha River back-arc basin was closed and the Zongza block collided with the Jomda arc; in the Late Jurassic-Paleogene, the Baoshan and Chuka blocks collided with the Lancang River arc, thus forming the Yanshanian-Himalayan granite belt in Zayu and Tengchong.