The wet and dry changes in paleoclimate is an important research content in study and reconstruction of paleoenvironments during geological history, while the paleo-precipitation is an important indicator of wet and dry zonation of the land surface climate. According to global and Chinese modern plant leaf carbon isotopes(δ₁₃^C_leaf) data, it is believed that the δ₁₃^C_leaf values of the C3 plant are controlled by the magnitude of precipitation, with positive δ₁₃^C_leaf in arid zones and negative δ₁₃^C_leaf in humid zones, and it is straightforward to calculate mean annual precipitation (MAP) by using logarithmic equations of δ₁₃^C_leaf versus MAP. Previous studies shows that the nC₂₇, nC₂₉, and nC₃₁ spectral peaks in the saturated hydrocarbon chromatograms are typical markers for the identification of organic matter from terrestrial plants sources in sedimentary strata, and the δ₁₃^{C of these n-alkanes(δ}₁₃^C_n-alkanes) records the carbon isotopic signals of the leaf of the plants(δ₁₃^C_plant), therefor it is possible to calculate and reconstruct the terrestrial plant leaf carbon isotopes(δ₁₃^C_leaf) after calibrating the effect of pedogenesis and diagenetic. Finally, based on the isotopic fractional coefficient (Δ‰=δ₁₃^C_CO2 -δ₁₃^C_planr) between paleo-atmospheric CO₂ (δ₁₃^C_CO2) and the plant (₁₃^C_plant), and by using the fitting equations of Δ‰ values to MAP (mm/yr) which was established in this paper, we quantitatively calculated the paleo-precipitation and delineated the dry/wet changes of the paleoclimate during the deposition process of the section, and we also discuss the influence of latitude, altitude, and temperature on the reconstruction results. The Cenozoic climate in China has undergone significant changes, which was manifested by the climate was controlled by the planetary wind system in Paleogene, while it evolved into a monsoon climate in Neogene. In this paper, we reconstructs the variation curves of paleo-precipitation correspond to the succession from Eocene upper member of Xiaganchaigou Formation to the Quaternary Qigequan Formation of the Fengxi 104 wells (4514m ～530m ) in the Qaidam Basin. The result showed that during the deposition of the Oligocene Shangganchaigou Formation, the Qaidam Basin receivedStheSleastSamountSofSprecipitation of only 250 mm/yr, while during the deposition of Pliocene Shizigou Formation, the Qaidam Basin receivedSthe maximum precipitation which is up to 1200 mm/yr, thus we proposed that the increase of precipitation in 8Ma may be related to the emergence of the Asian monsoon and the climate humidification in China.