As an important component of proteins, nucleic acids, enzymes and chlorophyll nitrogen (N) is a crucial element for ecosystem function. Many large research programs undertaken by the International Geosphere and Biosphere Program (IGBP) and the Intergovernmental Panel on Climate Change (IPCC) have included the N cycle as part of their core research. Globally, grassland ecosystems play an extremely important role in maintaining global and regional ecological balance. To date, few studies on the response of the N cycle to global changes have been conducted. There is some urgency to determine the effect of elevated atmospheric CO_2 and temperature, precipitation change, nitrogen deposition and human activities (grazing, cultivation, fire, etc.) on the N cycle in grasslands. This paper reviews research progresses in China and globally on the effects of global change and human activities on the key N cycle processes in grassland ecosystems. Additionally, issues requiring research emphasis are identified.