Stable isotopes in precipitation are valuable tools for investigating large-scale atmospheric circulation and regional hydrological cycles. The Tanggula Mountains (TGM) are a crucial climatic boundary within the monsoon transitional zone of the Tibetan Plateau (TP). However, the potential mechanisms controlling precipitation stable isotopic variability in this key region remain poorly understood due to the lack of continuous isotopic observations. In this study, 406 precipitation samples were collected during the warm season from 2013 to 2021 at an exceptionally high-altitude site in the middle of the TGM to examine isotopic variations and controlling factors of precipitation across multiple timescales and precipitation types. The results revealed remarkable seasonal and interannual variations in precipitation isotopes in this monsoon transitional region. The stable isotopic compositions among different precipitation types exhibited pronounced differences, with rain showing notably lower isotope values than graupel and snow. A significant amount effect on precipitation isotopes was observed across various timescales and precipitation types. Additionally, a significant inverse temperature effect was identified in daily precipitation isotopes. On a monthly timescale, precipitation isotopes showed a coexistence of temperature and inverse temperature effects, reflecting the alternating effect of different atmospheric circulation systems on precipitation isotopes. Statistical analyses quantitatively demonstrated the effects of different moisture sources on precipitation isotope variations. Specifically, Indian summer monsoon moisture was distinctly characterized by a pronounced depletion of heavy isotopes, in contrast to westerly moisture, which exhibited a relative enrichment of heavy isotopes. Teleconnection analyses revealed that precipitation processes in the moisture source regions and along transport pathways influence the isotopic composition of precipitation on the central TP. These findings provide a critical foundation for interpreting paleoclimatic records and understanding regional water circulation processes in the monsoon transition zone of the central TP.