In arid and semi-arid areas, water is an important factor that restricts the growth of trees. Due to the scarcity and uneven distribution of precipitation, the leaf absorption of water is the main way for trees in this area to absorb and use small amounts of precipitation and condensate. The mountainous area of Beijing is located in an ecologically fragile zone prone to drought and less rain. Forest vegetation often suffers from drought stress. Therefore, for the forest system in this area, the direct absorption and use of intercepted rainfall by leaves is an important way for trees to obtain water during dry periods. Based on field comparative control experiments and indoor pot plant simulation experiments, Platycladus orientalis, the main afforestation tree species in Beijing mountainous areas, was selected as the research object. Natural rainfall and simulated rainfall experiments were carried out to study the water absorption characteristics of Platycladus orientalis leaf before and after rainfall, and explore how Platycladus orientalis under arid environment alleviate drought stress by absorbing water by leaves. The results show that when Platycladus orientalis is under drought stress for a long time, the leaves can use rainfall to alleviate the drought stress of trees; the water absorption capacity of leaves is positively correlated with rainfall intensity and negatively correlated with soil moisture content; Under severe drought, Platycladus orientalis plants have the most obvious water absorption phenomenon when the rainfall intensity is 15 mm/h. The maximum change in leaf water potential is (1.18±0.17) MPa, and the maximum change in leaf water content is (8.47±1.00) mg/cm²; When the soil moisture content is higher than 20.8%, there is basically no water absorption by the blades. The test results show that leaf water absorption in arid areas is an important source of water for trees in addition to root water absorption, and it is of great significance for effective use of scarce water resources in arid areas and alleviating plant water deficit.