Abstract: Mineral magnetic measurement was applied to the lake sediment core Chao-Ⅱ derived from the northeast shore of Dianchi, Yunnan Province, as a case of paleoenvironmental study on the basis of magnetic stratigraphy. The results show that there are two significant changes of magnetic minerology around depth 0.9 m and 6 m, respectively. Combining these preliminary results with the analysis of pollen content, particle constitution, geochemistry,mineral component as well as radiocarbon chronology, an outline of the environmental changes in Dianchi Lake is proposed in the paper, which indicates that Dianchi Lake was bigger in the Late Pleistocene than present and considerable scale of lake transgression happened around the end of the Pleistocene. It is suggested that the surface of Dianchi Lake began to reduce from the Early Holocene, corresponding to the climate change of Kunming Basin.