Abstract: This paper is to explore the issues of scale effect of water saving,caused by the returning f lows and their reuse in the water resource system Taking the rice-based irrigation system,Zhanghe Irrigation System(ZIS),as an example,we analyzed the components of water balance and their roles at different scales,and point out that the situation would be become more complicated and the scale effect could be obvious with the increas of scale Based on the experimental and long-term historical data in ZIS,we consider water use at different scales——the fields,the middle scale,a main canal-commanded area scale and the irrigation system The results demonstrate the higher water productivity under water saving irrigation practice at the field scale and in the ZIS.And there are real water saving and the considerable increase in water productivity over time.