Alkali - aggregate reaction(AAR) is disadvantageous to durability of concrete. The Shankou Reservoir Project in Xinjiang province will adopt nearby natural aggregates, which contain AAR property. In order to under stand the AAR performance of the aggregates, study approaches include petrographic method, accelerated mortar bar method and inhibiting effect test. The results show the aggregates contain alkali reactivity. To insure safety of the dam, the alkali content of cement must be controlled strictly, or the additional amount of fly ash is not less than 20%. 