Situated at the southeast margin of the Tibetan Plateau, the Yunnan region is pivotal for investigating Late Cenozoic climatic changes. While considerable research has focused on the paleoclimate and paleoenvironmental evolution of Yunnan, the understanding of climate change from the Late Miocene to Pliocene primarily relies on carbon isotope and pollen records. Consequently, there is a dearth of high-resolution, continuous paleoclimatic records documenting humidity changes during this period. This study utilizes sediment cores from the Late Miocene to Pliocene in the Zhaotong Basin, northeastern Yunnan Province. Through sediment grain size analysis, the sedimentary sequence, lithological characteristics, and sedimentary structures indicate that the Zhaotong Basin was predominantly characterized by swamp-subfacies sedimentary environments during 8.8-6.2 Ma, transitioning to shallow lake subfacies during 6.2-2.8 Ma, and lakeside subfacies during 2.8-2.6 Ma. Grain size parameters of sediments in the Zhaotong Basin exhibit a drying trend of the South Asian monsoon during the Late Miocene to Pliocene. Combined with clay mineral and chemical weathering results from borehole data in the early period, it is inferred that the South Asian monsoon gradually weakened from the Late Miocene to Pliocene, primarily influenced by global cooling and decreasing global CO₂ concentrations.