Recycled concrete research is one of the hot points at home and abroad currently. Whether the recycled concrete can be used in construction or not depends on its strength. Mixture ratio is an important factor deciding strength, while in which, the water cement ratio is one crucial parameter. So the calculation of unit water use in recycled concrete becomes an important research topic. The form of mixed coarse aggregate adding natural sand has already been studied by authors, the calculating formula for increasing water use has been put forward, but the calculation in other else case of aggregate combination form is not discussed. In this paper, the calculation for unit water use in recycled concrete in this case is discussed in detail, which can be used as a reference for designing the recycled concrete mixture ratio.