Gaize Basin located at in hinderland of Tibetan Plateau, whose sediments recorded significant palaeoclimatic information of Tibetan Plateau. Carbon and oxygen isotopes of Kangtuo Formation in Gaize Basin were test in this study. The results indicate that Gaize Basin experience two evolution phases during Middle-Late Eocene: ① the Middle Eocene open lake under humid climatic setting: In this period, carbon and oxygen isotope are strong depleted and just positive shift in oxygen isotope values at 43 layer. And the correlation between carbon and oxygen isotope variations is low (R2=0.082). These records indicate that Gaize basin is an open lake with abundance inflow water in humid climate during this phase, although it has experience a short term strong evaporation or decrease of inflow water. ② the Late Eocene closed basin in dry climate: In this phase, oxygen and carbon isotope become enrichment, consistently. And, the correlation coefficient between carbon and oxygen isotopic variations is high (R2=0.7762). Inferred from these records, Gaize basin experienced strong evaporation in arid climate, and, shrunken into a closed basin, gradually. The Late Eocene aridification is a regional event in the hinderland and northern of Tibetan Plateau, based on the previous paleoclimatic studies. Analysis of the uplift of Tibetan Plateau, Global paleoclimatic records, seawater strontium isotope curve and global PCO2 curve, the Late Eocene aridification could be mainly affected by the uplift of Tibetan Plateau.