Abstract: Populus tomentosa is a common green tree species in northern China, which has the characteristics of fast growth and strong water adaptability. Riverside shelter forest formed by Populus tomentosa plays an important role in preventing wind and fixing sand, retaining soil and water, greening and beautifying, and blocking non-point source pollution. By using hydrogen stable isotope tracer method, this paper selected Populus tomentosa on the bank of middle reaches of the Chaobai River as the research object, and measured the hydrogen stable isotope ratio(δD) of its stem water and potential source water(rainfall, soil water, groundwater and river water). By using multivariate linear mixed model, the contribution rates of various water sources were calculated. Combining with environmental factors such as rainfall and soil water content, the variation of contribution rates of various water sources were analyzed. Then water source characteristics of Populus tomentosa were concluded. The results showed that: ① The Populus tomentosa 50 m from the riverbank and farther away used water from rainfall, soil water, groundwater and river, which use soil water as a main source and followed by rainfall, groundwater and river water. ② The contribution of rainfall to Populus tomentosa increased with the increase of rainfall; ③ The influence of rainfall on the performance of the contribution rate of Populus tomentosa soil water lied in the change of soil water contribution rate within and between soil layers. With the increase of rainfall, 0～20 cm shallow soil water contribution rate showed an increasing trend, and 20 ～ 50 cm soil water contribution showed a decreasing trend. When the rainfall increased sharply, soil water contribution rate change between different soil layers.④ The influence of the distance from the river bank on the water source of Populus tomentosa was mainly manifested in the contribution rate of groundwater and river water and the overall structure of soil water contribution rate of different soil layers. The contribution rate of groundwater and river water decreased with the increase of the distance from the river bank. 50 m from the riverbank, Populus tomentosa used water in different soil layers equitably. 200 m away from the river bank, the contribution rate of soil water in various soil layers to Populus tomentosa decreased from shallow to deep, and 400 m away from the river bank, the contribution rate of deep soil water in depth of 50～ 100 cm was the highest.