Study region: western Loess Plateau, China Study focus: Stable isotopes are vital for understanding regional water cycle processesbut the dynamic variations of vapor (delta O-18(v)) and precipitation (delta O-18(p)) isotopes at different time scales remain unclear due to a lack of high-resolution data. This study systematically investigates these aspects using three years of continuous isotope observation data. New hydrological insights for the region: The average delta O-18(v) was -18.03 parts per thousand and delta O-18(p) was -7.93 parts per thousand, with delta O-18(p) consistently more enriched than delta O-18(v). On the monthly scale, delta O-18(v) enriched from January to May, peaked in June, then fluctuated downward until December. On the hourly scale, delta O-18(p) fluctuated significantly, while delta O-18(v) remained stable. The strongest correlation between delta O-18(v) and delta O-18(p) occurred on the day of precipitation (r = 0.55, p < 0.05). delta O-18(v) showed a significant precursor effect on delta O-18(p), with the strongest correlation at a lag of -2d, and the delta O-18(p) signal continued to modulate delta O-18(v) for about + 3d after the event. Temperature significantly impacted isotopes during the winter and transition monsoon periods, while the summer monsoon period was mainly controlled by moisture transport processes. Moisture transported caused gradual depletion of delta O-18 due to rainout effects. Additionally, strong convection in upstream regions led to isotopic depletion, with local convection also playing a key role. This study provides a theoretical basis for understanding the response mechanisms of water cycles in the arid-semi-arid transition zone under climate change.