Precipitation on the Tibetan Plateau (TP) have received attention because of its importance for regional water cycle. Based on data of 96 meteorological stations from 1961 to 2017 on the eastern TP, the relationship between the lead mode of summer (JJA) precipitation variability and the North Atlantic Oscillation (NAO) is analyzed, and the possible mechanisms for the unstable relationship are explained. The results show that the NAO dominates the leading mode of summer precipitation on the eastern TP, but there are interdecadal variations in their relationship, with NAO leading to a north-south dipole pattern in the early period (1961-1993), and a monopole pattern in the later period (2002-2017). The NAO is able to stimulate potential height anomalies with a quasi-barotropic structure in the upper layers over the TP, and form corresponding circulation anomalies in the lower layers, which in turn affect the water vapor anomalies in the region. During the early (later) period, the west edge of the NAO-related circulation anomalies is located in the northeastern (northwest) TP, which is conducive to the formation of precipitation anomalies of north-south dipole pattern (monopole pattern) in the eastern TP. The shift in the leading modes of summer precipitation on the eastern TP resulted in an abrupt change in the NAO-precipitation relationship in 1998 for the entire study period. Given the nonstationary relationship between NAO and summer precipitation on the eastern TP, the interdecadal background signal needs to be considered in the study of NAO’s impact on regional climate in order to improve the prediction level and model simulation capability.