Information on the palaeocnvironment from Late Pleistocene to Holocene in northwestern Yannan Plateauhas been deduced from a study of a 28.81m-long core taken from Napahai Lake. The results from Relative Brightness Index (RBI) as well as those from the lithological analyses of bulk sediments, total organic carbon and granulometric analyses have been used to reconstruct the environmental and climatic evolution of the area. The ages were provided by three14C datings. The record suggested a climate fluctuation between warm-dry and cool-wet from ca. 57 to 32ka B. P., whichled a shallowing and swamping of the lake. The water level again increased quickly at ca. 32ka B. P., reached it's peakduring LGM (Last Glacial Maximum, ca. 18-20ka B. P. ) and remained relative high until ca. 15ka B. P. The high water level at LGM is attributed to cold-wet conditions. The area experienced an abrupt and unstable climatic changes during the transition period from 15 to 10ka B. P. with a dominated littoral environment. A warm-dry climate led to the contraction of the lake during the Holocene and reed-swamps became dominant. After a minor wet-cool pulse during the LateHolocene, the modem climate became to be established.