Abstract: Many mistakes existed in reasonable collocation of water resources, because of misapprehension about the quantity of water resources, are often found in the water resources programming at present. Especially modern water resource programming consider the ecological use for water resources, there are fuzzy cognition about the relation between the quantity of water resources and the water quantity for ecosystem use. At first, general concept and composition of the quantity of water resources have been introduced in this paper. And then, the concept and computation method of the water quantity for ecosystem use have also been introduced. Based on these analyses, the paper emphasizes to introduce how to consider the problem of the ecological use for water resources in water resources programming. It is a support to water resource programming proceeded in the whole China. The main results include： (1) Composition and conversion of the quantity of water resources have been summed up as a figure. (2) The concept and calculation method of the water quantity for ecosystem use have been given in the paper. You can find two methods about calculation of the water quantity for ecosystem use. (3) The relation between the quantity of special water resources and the water quantity for ecosystem use is cross. The calculation of special water resources is based on the water quantity for natural ecosystem use. On the other hand, the artificial ecosystem use must be considered during the collocation of water resources. (4) According to the different use for ecosystem quality, the water quantity for ecosystem use can be divided as：tallest ecosystem use, lowest ecosystem use, and reasonable ecosystem use. According to the condition of ecosystem, the water quantity for ecosystem use can be divided as：the present ecosystem use, target ecosystem use, and natural ecosystem use. (5) To water resources programming, we suggest：to adopt reasonable ecosystem use to decide the ration of the water quantity for ecosystem use. In the region of better ecosystem, the water quantity for ecosystem use can be calculated according to the present condition. However, in the bad region, target ecosystem use should be considered.

Key words: water resources programming, water resources, the water quantity for ecosystem use, reasonable collocation of water resources