The Yellow River Delta (YRD) is located in northeast Shandong province. It is formed by perennial deposition of sediment and frequent diversions of the Yellow River. YRD has many ecological system types, including farmland, grassland, and wetland and so on. The wetlands can be subdivided into meadows, marshes, and beaches. These areas have been the habitat and transfer stop of migratory birds, which makes it important for protection of biodiversity. It is also important as an ecological protective screen between inland and the ocean. However, YRD is facing new challenges from both nature and society; on the one hand, the storm tide, seawater intrusion, drought, and primary soil salinization make the area have a vulnerable ecologic foundation; on the other hand, the abundant land and oil resources have led to intense human activities. The primary ecological environment has been heavily fragmented because of destruction from farming and oil exploration, and the destruction further has led to a high secondary soil salinization degree and rapid expansion of the vulnerable area. All this makes it necessary to understand and grasp the current situation of the ecological environment in YRD, which is helpful for regional ecological environmental protection and development planning. The aim of this study was to evaluate the ecological vulnerability degree in YRD and then analyze the spatial characteristics and reasons for these characteristics according to the assessment results. The selected assessment method in the study was the fuzzy analytic hierarchy process (FAHP), which is the combination of the fuzzy evaluation method (FEM) and the traditional analytic hierarchy process (AHP). FAHP combines the strong objectivity of FEM and the clear structure of AHP. This assessment process was more reasonable than other methods. Additionally, the fuzzy logic model was selected for the quantitative expression of the indicator grading and evaluation results, and was different from traditional grading methods that have strict quantity boundaries. Twenty-one evaluation indicators were selected from underwater status, soil condition, land use, landform, vegetation coverage, meteorological conditions, ocean influence, and social economy according to the "pressure-state-response" framework in AHP. The study result showed that the spatial distribution of ecological vulnerability of YRD had a strong regularity. Generally, the vulnerability degree gradually decreased from the coastline to inland, and the best ecological environmental status was around the crossing of the Yellow River and the Diao River. In the coastal area, the vulnerability degree was lower where there were seawalls than where there were none, while in the inland, the ecological environment was better along the rivers than in other areas, especially the areas where human activity was frequent such as farmland, aquaculture areas, and saltpans, where the vulnerability degrees were very high. Along with those artificial reasons, the regional soil and ground status were also bound up with ecological vulnerability, and the spatial correlations between soil quality and ground water level were -0.55 and -0.74 respectively.