The Western -Line South -to -North Water Transfer Project is planned to transfer water from Tongtianhe River,Yalongjiang River and Daduhe River(following called'three rivers')into the Yellow River in order to solve the problems of drought and water shortage existing in the northwest area and the northern parts of China.The transferable water by means of the water transfer project is the basis for developing various works.Based on the available data and by analyzing the factors of runoff at water diversion dam-site,water use demand on the upstream and downstream of water diversion dam-site,the release rate of reservoir,the project scale and so on,the level of effect of each factors on the transferable water has been put forward and the suitable transferable water of respective water diversion dam-site have also been estimated.