Abstract: Abstract：Based on a field survey and analysis of environmental proxies (magnetic susceptibility, grain size, carbonate content, ESR ages etc.), the paper discusses the change of the depositional environment at the Guge Formation section in the Zanda basin, Tibet, at 4.40-2.74 Ma. The analytical data show that remarkable changes in depositional environment took place in the Zanda basin after the Xiangquan movement at 4.4 Ma: the depositional environment changed from the fluvial facies in the early stage to the lacustrine facies in the late stage, forming a thickness of more than 500 m of sediments of the Guge Formation. It reflects the changes of the sediments in the Zanda paleolake from the lakeshore→shallow lake→semi-deep lake→lakeshore-shallow lake, i.e. the entire process from the emergence→development→extinction of the paleolake. Its growth process is closely related to the plateau uplift and climatic and environmental changes since the late Cenozoic.