Abstract: The rocky mountain areas in Northern China are confronted with water resources scarceness due to the sustainable development and utilization of the precious resources. To effectively utilize limited water resources, the isotope techniques are widely used to study the movement of water in hydrological cycle. The study was conducted at the Jiufeng low mountain region of West Beijing. We identify the transforming relationships among those water sources in Jiufeng through analyzing the isotopic variations of precipitation, soil water and spring water. Results show that the water line in rainy season in Jiufeng is significantly different from the local meteoric water line in Beijing, both slope and intercept of the water line in rainy season are smaller than that of the local meteoric water line, along with the rain, the characteristics of D and ¹⁸O have scheduled changes and rainfall effect, and the scheduled changes in precipitation also affect the soil water isotopic characteristics. The isotopic compositions of soil water are relatively concentrated in the study region. Both slope and intercept of evaporation line equation are smaller than that of the local meteoric water line and the rainy seasonal water line. The soil in Quercus Variabilis Mixed Forest is not sensitive to small precipitation events. The soil water movement in Platycladus Oriatalis plots is faster than that in Quercus Variabilis Mixed Forest, which can account for the affection of forest types and soil characteristics to the conversion between different water sources. The isotopic composition of spring water is relatively stable, and they mainly distribute on the bottom right of the local meteoric water line, near the intersection point with the rainy seasonal water line. There have different isotope variations among different water sources. The largest variation is in rain water and the least is in spring water. The values of hydrogen and oxygen isotopes in different water sources decrease with the water cycle path from precipitation to soil water, and then to ground water.