During the initial construction stage of Danjiangkou Dam, a certain number of reactive aggregates(flints) were found in the concrete and hence posed potential risks caused by possible Alkali-Aggregate Reaction (AAR). In this paper, microscopic tests on the original core samples and cured core samples are carried out to judge the status of AAR accurately. The test methods include Scanning Electron Microscope Analysis (SEMA) and Energy Dispersive Spectrometry Analysis (EDSA). The analysis results show that AAR deterioration hasn’t been found since 40 years of dam operation due to proper preventive measures. Nonetheless, AAR is still likely to occur if three indispensable elements exist, namely certain number of reactive aggregates, available alkalis, and water. It is concluded that besides taking proper control measures to the concrete of heightened part, the impermeability of the whole dam should be enhanced for longterm durability and safety of the dam containing alkali reactive aggregates.