The alkaliaggregate reaction in concrete is one of the adverse reactions that result in the diseases of the structures of cement concrete. The article expatiates on the features and influence factors of the alkaliaggregate reactions. On basis of observations, investigations, core drillings and chemical tests of the engineering case, the article makes detailed analysis on the mechanisms and processes of the alkaliaggregate reactions in concrete. Finally, the article provides some recommendations for the prevention of the alkaliaggregate reactions in concrete.