The long-term precipitation trend over the Tibetan Plateau (TP) was studied using a high spatiotemporal resolution precipitation dataset. It was found that the warm season (May–Sept.) precipitation over TP increased significantly during 1981–2015 (grid-mean: 0.9 mm/a), which was most significant in the northeastern, central, and western TP. The geopotential height field of 500 hPa over TP was divided into 9 circulation patterns (T1–T9) by using the obliquely rotated Principal Components in the T-mode (PCT) method, in which T2 and T4 were the dominant circulation patterns (DT) for the increase of precipitation. The geopotential height field of DT was low over the west but high over the east. DT dominated the increase of precipitation was reflected in the increase of precipitation days and daily precipitation. The increase in the number of DTs led to increased precipitation in the central and western TP. Another dominant mechanism was the optimization of precipitation conditions: T2 was dominated by the optimization of dynamic conditions driven by the larger gradient of geopotential height, and T4 was dominated by the optimization of thermal conditions driven by more water vapor.