Abstract: Water availability has been ever increasingly constrained for the growth of vegetation against global warming in recent years. Ecological restoration has launched in the Loess Plateau, such as "The Grain for Green project". However, the overconsumption of water resources has caused to degrade the vegetation, due to the excessive restoration. New ecological issues have been emerged as the severe drought in this region. This study aims to investigate the current status and variations in the water surplus and deficit index (WSDI) in the Loess Plateau. Effective solutions were then proposed to overcome these issues. Among them, the WSDI was defined as the ratio of effective precipitation to evapotranspiration. The data was collected from the remote sensing and ground observations from 2001 to 2023. A systematic analysis was made on the spatiotemporal patterns in the temperature, precipitation, effective precipitation, evapotranspiration, normalized difference vegetation index (NDVI), and gross primary productivity (GPP). The key driving factors on WSDI were also determined to clarify the current state of water surplus and deficit in the region. The results revealed that: (1) The Loess Plateau exhibited a tight balance in the WSDI on an annual scale over the past 23 years, with a long-term average WSDI of 1.1. The average annual precipitation was 441 mm. While the evapotranspiration that related to vegetation reached 353 mm. There were the significant seasonal variations in the WSDI. The winter experienced the most severe water deficit, followed by spring. In contrast, the summer and autumn shared the water surplus. (2) Both effective precipitation and evapotranspiration showed an upward trend. However, the rate of increase in evapotranspiration surpassed that of effective precipitation, resulting in a downward trend in the WSDI at various time scales. The most outstanding decline was observed in the summer months. Spatially, 91% of monitoring stations displayed a declining trend in the WSDI at the annual scale, especially during the summer. (3) Different types of vegetation were varied greatly in the WSDI. Grasslands showed the fastest decline in the WSDI during the spring. While the shrublands were experienced the most significant changes in summer. There was the relatively minor variation in the autumn and winter seasons. Both shrublands and croplands exhibited the outstanding declines. (4) The WSDI was depended mainly on the complex and nonlinear relationship among the temperature, precipitation, and vegetation. There were the both direct and indirect effects of the precipitation on the WSDI. The precipitation variability was made the greatest contribution. Additionally, the WSDI was dominated by the productivity of vegetation in summer. This finding can offer the vital insights into the farmland water resources and vegetation restoration. The allocation of water and soil resources was also optimized in the Loess Plateau. Particularly, the dynamics of water surplus and deficit can greatly contribute to the decision-making on the sustainable ecological practices and climate challenges in future.