The H and O isotopecompositions of the Yangtze River water was investigated on the samples collected from 25 hydrological stations in the mainstem and 13 hydrological stations in the main tributaries during 2003～2007.Large variation ranges were observed for D(-30‰～-112‰) and -3.8‰～-15.4‰)。Along the river cource(from the river head to the river mouth), the H and O isotope compositions of the river water collected in different time period desplay always a similar variation pattern, i. e. the Dand  values decrease graduary from the river head to the Panzhihua station and then increase graduary from the Panzhihua station to the river mouth. It is found that the meteorical water is the most important factor to control the Dand  values of the Yangtze River water. The Dand variation trend from the Panzhihua station to the river mouth is parallel to the Dand variation trend of the meteoric water in the drainage area. The difference of Dand compositions between various tributaries and its effect to the Dand O of the mainstem reflects also the constraint of the meteoric water to the Yangtze River water. Evaporation has also important effect to the H and O isotope compositions of the Yangtze River water.The river head of the Yngtze is located in the Qinghai-Tibert Plateau,where lakes and marshes are very abundant.Due to very dry weather and strong sunshine,the water in lakes and marshes experinced longterm evaporation will have higher salinity and heavier and O isotope compositions. The water Input from these lakes and marshes into the Yangtze River will effect the and O isotope compositions of the river water. It is found that evaporation can also raise the D and 18O values of the water of Dongting and Poyang lakes during the dry season and lead to a incease of the D and 18O values in the water of related section of the Yangtze. The melting of snow and ice is also an important factor effecting the and O isotope compositions of the Yangtze River. The snow and ice melting water is an important source in the river head and the heads of all tributaries, that flow into the mainstem of the Yangtze from left side. Due to the snow and ice melting water has unique H and O isotope composition, the contribution of this kind of water can effect the H and O isotope composition of the Yangtze River water. The Three Gorge Dam has huge influence on the hydrodynamic system of the Yangtze and the effect of Three Gorge Reservoir to the water resource of the Yangtze is waiting for long term monitoring.According to the data of this study, the Three Gorge Dam has little effect to the H and O isotope composition of the water in related section of the Yangtze in the high water season. However, it show clear influence to the H and O isotope composition of the water in section from Yichang to Shashi in the low water season by changing the contribution of different water sources . The present state and variation trend of water resource of the Yangtze is a very important topic that receive high attention of various parties.For getting better understanding on this issue, we need to know more on the correlation between variation of water resource and various meteoric and hydrological factors and the interaction between river water and other waters, such as the meteoric water, underground water, lake water and ice and snow melting water。The H and O isotope tracing method can play a key role for solving these problems. As the available data are still limited, we can not trace the variation trend of the meteoric and hydrological conditions of the Yangtze River area by the H and O isotopes in detail at present. However, we believe that a conbination of proper H and O isotope study with conventional meteoric and hydrological investigation can be very helpful to understand the variation trend of water resource in the Yangtze River system.