As in the case of most ecosystems, freshwater wetlands can be affected by climate change, which can alter wetland hydrology, water quality, and ecological health. Freshwater wetlands provide a number of valuable ecosystem activities, including carbon sequestration, primary productivity, floodwater storage, nutrient processing, and sediment stabilization. Further, they contribute to the high biodiversity of vegetation, macro invertebrates, fish, amphibians, reptiles, birds, and mammals. The Nenjiang Basin is one of the most important crop-production regions in China. A large portion of the headwaters of the river's basin is located at relatively higher latitude and higher altitude regions, and the natural wetlands occupy approximately 15% of the total area of the Nenjiang Basin, supporting a large number of terrestrial and aquatic organisms. However, since 1978, approximately 28% of the wetland area has been drained and converted into agricultural fields or urban development land. The conversion of wetlands for agricultural purposes and urbanization has created considerable stress on the ecological health of the Nenjiang region. Although the effects of climate change are not yet fully understood, it could be an additional source of stress for already deteriorated regional ecosystems because of the reductions in the wetland area. In addition, since the natural wetlands of the Nenjiang Basin occupy a large area, it is also one of China's most important wetland preservation areas. This area has experienced substantial changes in climate and land use/cover, which has led to serious water resource problems. Recent studies have shown that the regional climate has become warmer and drier, and the runoff in the Nenjiang Basin has declined since the 1950s. The predicted wetland ecological water requirements were 70.284 billion m³, 118.696 billion m³, and 169.343 billion m³ during high precipitation, flat precipitation, and low precipitation years, reflecting its correlation with the climatic conditions. Furthermore, changes in the annual maximum temperature, annual minimum temperature, annual average temperature, and precipitation were calculated from 1906 onward and projected to 2100. The annual minimum temperature showed a relatively significant increasing trend compared to the other measured factors, especially the annual maximum temperature. The changes in the maximum temperature and minimum temperature, resulting in narrowing of the diurnal temperature range, could cause the crop growth cycle to delay or advance. On the basis of the previous calculation, we selected the fifth phase of the Couple Model Intercomparison Project (CMIP5) simulations of global climate models to predict the wetland ecological water requirements from 2030 to 2100. In addition, three climatic emission scenarios were chosen, Representative Concentration Pathways (RCP) 2.6, 4.5, and 8.5. The results showed that the maximum temperature, minimum temperature, and precipitation jointly affected wetland ecological water requirement. Specifically, wetland ecological water requirement under RCP2.6 scenarios showed a decreasing trend after an initial increase, while the RCP4.5 and RCP8.5 scenarios showed an increasing trend in which by 2100, the wetland ecological water requirement reached 147.337 billion m³ and 132.659 billion m³, respectively. We believe that future studies must focus on how to coordinate and balance the water requirements and maintain the sustainable development of wetlands.