Studing the effects of changing precipitation regimes and increasing nitrogen deposition on the key processes of nitrogen cycle in grassland ecosystem and exploring the additive effects and the adaptation characteristics of them responding to the future global climate changes were helpful to provide scientific basis for regulating nitrogen transformation processes, improving grassland nitrogen use efficiency and reducing the negative ecological effects. In this paper, different effects induced by water and nitrogen additions and their co-effects on plant and soil nitrogen pools were reviewed. Meanwhile, the possible drive mechanisms related to the changes in microorganisms and enzymes under these conditions were analyzed. On this basis, the uncertainties about the effects of changing water and nitrogen on the key processes of nitrogen cycle in grassland ecosystem as well as the main problems existing in current related studies were also discussed.