Abstract: Ever since T.E. Stanton in 1940 first observed and diagnosed the Alkali Aggregate Reactions (AAR) in concrete, Alkali aggregate reaction has become one of the important causes of concrete’s engineering damage. A great deal of researches have been done. Damages caused by AAR of hydraulic concrete and the significance of researches on AAR are reviewed. The principle and classification of AAR, testing methods and their innovation as well as comprehensive prevention measures against AAR are also introduced. These preventive measures include using non-active aggregate, controlling total alkali content in concrete, controlling humidity, adding inhibition materials and chemical additive. Problems that need to be resolved and suggestions regarding AAR researches are proposed.