Abstract: During the rainfall events in the rainy seasons of 2005-2007,a total of 87 water samples from rainfall events,soil water at 0-400cm layers,surface water in valleys,and ground water(spring water,well water) were collected,the D(deuterium) &¹⁸O(oxygen-18) in these samples were analyzed to interpret the relationship among those water sources in Yangou watershed in the loess hilly region,and the locally meteoric water line(LMWL) was obtained.The result shows that the LMWL of Yangou is similar to that of Xi'an region but different significantly from the LMWL of China and the global meteoric water line(GMWL),both slope and intercept of the LMWL of Yangou are smaller than that of China LMWL and GMWL,the δD &δ¹⁸O content in different water sources are gradually richer in the order of rainwater,ditch water,soil water and groundwater due to isotopic fractionation,and the enrichment of δ¹⁸O is faster than that of δD.The variation of δ¹⁸O and δD values can be used to identify different water sources and to determine the transformation relationships among them.We have found that the minimum values of δ¹⁸O and δD appear to be at the 180-200 cm depth,indicating that the precipitation can infiltrate into the subsurface soil at that depth and the influence of deep soil water on the surface evaporation vanishes at that depth too.The δD &δ¹⁸O values increase gradually below 200 cm depth,which suggests that the influence of precipitation infiltration is weakening and the groundwater component in soil water is increasing.In responding to rainfall the events,the δD &δ¹⁸O values are found to be fluctuated in deep soil at the 380-400 cm depth.This result indicates that the rainfall is able to recharge groundwater through either capillary micro-flow or/and priority macro-flow.The experimental data also show that the time lags between the rainfall events and recharging from the springs are less than 35 days.Further studies are warranted to investigate the time lags between rainfall events and recharging from wells,as well as the recharging amount of groundwater from soil water.