The middle reaches of the Heihe River serve as the most important commercial grain and cash crop production base in Gansu Province, supporting over 90% of the cultivated land and population of the entire Heihe River Basin. The regional eco- geological environment of this area is directly related to regional food security, ecological security, and sustainable socio- economic development. Given the background of water scarcity, fragile ecological conditions, and increasing pressures from human activities and climate change, this study aims to assess the regional eco- geological vulnerability of the area and provide scientific support for ecological protection and restoration.Methods: An AHP- PCA （Analytic Hierarchy Process—Principal Component Analysis） entropy weight combination model was employed to systematically evaluate the regional eco- geological vulnerability of the middle reaches of the Heihe River. 13 evaluation indicators were selected from 4 dimensions: topography and geomorphology, climatic environment, geological environment, and ecological environment. All indicators were normalized using range standardization, and the combined weights were determined by integrating subjective weights from the AHP and objective weights from PCA based on the minimum information entropy principle. The weighted linear combination method was then applied using ArcGIS 10.8 to generate the regional eco- geological vulnerability map.Results: The overall regional eco- geological vulnerability of the study area is relatively high. The areas of slightly, moderately, highly, and extremely vulnerable zones account for 14. 83%, 28. 99%, 35. 29%, and 20. 89% of the total area, respectively. The slightly to moderately vulnerable zones are mainly distributed in the oasis and oasis- desert transition zones, while the highly to extremely vulnerable zones are concentrated in the desert, gobi, and hilly areas. Weight analysis revealed that groundwater abundance (0. 1271), vegetation coverage (0. 1099), and soil type (0. 1053) are three key sensitive factors, collectively contributing 34. 23% to the vulnerability assessment. Furthermore, two typical feedback mechanisms were identified: a degradation- type positive feedback loop in the extremely vulnerable zones characterized by self- locking and difficult reversibility, and an “artificially maintained benign loop” in the slightly vulnerable zones that highly depends on continuous irrigation and management.Conclusions: This study developed an AHP—PCA entropy weight combination model suitable for regional eco- geological vulnerability assessment in arid inland river basins, effectively integrating expert experience with data characteristics. The findings reveal significant spatial heterogeneity in eco- geological vulnerability and quantify the dominant controlling factors. Based on the vulnerability levels and their driving mechanisms, differentiated ecological restoration strategies were proposed: in slightly to moderately vulnerable zones, priority should be given to optimizing water resource management and enhancing the resilience of oasis agricultural systems; in highly to extremely vulnerable zones, nature- based protection measures should be implemented with strict control of human disturbances. The results provide direct scientific support for ecological protection and restoration, territorial spatial planning, and sustainable development policy- making in the middle reaches of the Heihe River, and offer methodological references for similar arid inland river basins.