In order to study the inhibition effect and mechanism of metakaolin and fly ash on alkali silica reaction(ASR) in concrete，the extension of mortar bar made with activity quartz glass aggregate and super metakaolin powder to cement(5%，10%，15%，20%，25%) and fly ash to cement(10%，20%，30%，35%，40%, 45%)mixtures were measured and evaluated in alkali solution according to accelerated mortar bar test(AMBT). The mechanism of the effect was studied by scanning electron microscope(SEM) analysis. The results show that small amount of super metakaolin powder exerts significant influence, whereas only when the proportion of fly ash is up to 35%, can it control alkali silica reaction effectively. As super metakaolin powder particles are much smaller than fly ash particles, they have higher activity.