Abstract: Owing to the increase in crop planting area and proportion of water-intensive crops, the imbalance between the water supply and demand for grain production has been exacerbated in the three provinces of Northeast China (NEC). As the main water resource for grain production in NEC, the green water plays a pivotal role in alleviating this imbalance. In this study, we aimed to quantify the green water deficit (GWD) of major grain crops (rice, corn, and soybean) in NEC at multiple spatial and temporal scales. To this end, we analyzed meteorological and crop data from 2001 to 2020 to calculate the GWD in the whole growth period and the critical growth periods of the three crops using the Penman-Monteith equation. The results showed that the GWD of rice during the whole growth period ranged from 50 to 125 mm in wet years, exceeded 230 mm in dry years, and exceeded 400 mm in dry years in the western Songnen Plain and southwestern Sanjiang Plain, which are the regions with the highest GWD for rice. The green water supply for corn was sufficient during wet years, but insufficient during dry years with an average deficit of 70 mm. Spatially, the GWD was smaller in the mountainous regions and larger in the plains, and showed a decreasing trend with time in the plains. The green water supply for soybeans was relatively adequate, but the southern Songnen Plain and southwestern Liaohe Plain still had a deficit of green water in some individual years. We also analyzed the GWD at critical growth periods of each crop to characterize the seasonal GWD. In general, rice, corn, and soybean had GWDs in critical water demand periods in 80%, 85%, and 40% of the study years, respectively. Notably, the critical water demand period for corn was also its severe GWD period, indicating that the adverse impact on corn yield may be relatively higher, as it is mainly a rain-fed crop in NEC. The most severe GWD period for rice was the tillering stage, with an average annual deficit about 70 mm. However, this deficit can be compensated by blue water irrigation. The largest seasonal GWD of soybeans occurred during the maturity stage, when its effect on yield is relatively small. Thus, seasonal GWDs had the greatest effect on corn yield. The interannual, seasonal, and regional differences in total amount of GWD (TGWD) were obvious. For example, the average TGWD was more than 20 billion m³ in dry years and less than 10 billion m³ in wet years. The TGWD of the Songnen Plain was larger, ranging from about 0.5 billion to 2.0 billion m³, followed by that of the Sanjiang Plain, whose TGWD was between nearly 0.5 billion and 1.2 billion m³. Overall, the gap between water supply and demand was lower in mountainous regions and higher in the plains, where crops are widely distributed. Therefore, the water supply deficit in the plains places continuous pressure on water resources in NEC. The results of this study contribute to our overall understanding of water-crop relationships and provide scientific information for agricultural water management in NEC.