Ecological water diversion(EWD) is a primary measure for rehabilitating degraded ecosystems in inland river basins of arid regions; and the river water overflow induced by EWD project directly impacts the efficacy of oasis vegetation restoration. Integrating the Global Surface Water Dataset spanning from 1987 to 2021 as well as natural environment and human activity data within the basin, this study delves into the spatial and temporal shifts in the river overflow process and its influencing factors before and after EWD in the lower reaches of the Heihe River. This is achieved by the construction of water body frequency based on Google Earth Engine platform, which denotes the ratio of observed instances of a particular pixel to the total observed instances within a specific time. The findings revealed that before the diversion, the mean annual runoff at Zhengyixia, Shaomaying and Langxinshan station stood at 886×106, 528×106, and 427×106 m3, respectively, escalating to 1，199×106 , 812×106, and 670×106 m3 after the diversion; the mean annual runoff of Langxinshan to East Juyan Lake section amounted to 617×106 m3(representing the available water resources in the oasis), which concentrated mainly in periods of April-May and September-October. Spatially, the area of permanent water bodies progressively increased after the diversion, and predominantly clustered around the East Juyan Lake. In 2004, a permanent water body appeared in East Juyan Lake, while West Juyan Lake did not see the emergence of permanent water bodies. The highest water body frequency was observed in the vicinity of the Shaomaying-Langxinshan section, followed by East Juyan Lake and its periphery, while the East River, West River, and West Juyan Lake exhibited lower levels. Before EWD, river overflow was primarily a natural process heavily influenced by human activities in the middle reaches; however, it showed a significant positive correlation with ecological water volumes (P<0.01) after EWD. In addition, downstream annual evaporation and human activities were both significantly and negatively correlated with river overflow processes (P<0.01). It is recommended to construct and rehabilitate ecological hydraulic engineering projects in the lower reaches of the Heihe River to improve spatial and temporal imbalance of river overflow, and then ensure the health and safety of downstream ecosystems.