Stable hydrogen and oxygen isotopes are extensively utilized to investigate ecological hydrological processes, offering insights into water movement and plant transpiration. We conducted an analysis of the seasonal fluctuations in δ1?O enrichment within the leaves of Platycladus orientalis （?18OL） in a mountainous area, Beijing, focusing on dry season (May-June) and rainy season (July-August). Furthermore, we investigated the correlations between ?^18 O_L and a range of environmental and physiological variables. Additionally, we assessed the efficacy of the Craig-Gordon model, the 2-Pool model, and the Péclet model in simulating ?^18 O_L. The results showed that, in the rainy season, there were significant increases in precipitation, relative humidity, soil volumetric water content, transpiration rate, and stomatal conductance compared to the dry season （P<0.05）. ?18OL showed a daily variation pattern characterized by a "low-high-low" trend, with markedly elevated values observed during the dry season in comparison to those recorded during the rainy season （14.17±2.05‰>7.79±2.13‰）（P<0.05）. Temperature, vapor pressure difference, transpiration rate, and stomatal conductance exhibit significant positive correlations with ?18OL, whereas relative humidity demonstrates a significant negative correlation with ?18OL. Notably, during the rainy season, ea/ei was negatively correlated with ?18OL, while ?e showed a positive correlation with ?18OL. The high atmospheric humidity and soil moisture in the forest of Platycladus orientalis during the rainy season are the main reasons for inhibiting the increase of ?18OL.Craig-Gordon model tends to overestimate ?18 OL, whereas both 2-Pool model and Péclet model demonstrate a more accurate simulation of ?18OL. This study enhances the understanding of the seasonal variability in leaf water δ18O enrichment and its associated hydrological mechanisms. Additionally, it offers methodological references for evaluating the applicability of leaf water isotope enrichment models.