The influence of scrap rubber powder on alkali aggregate reaction（AAR） was studied by the mortar bar length method. The effect of rubber powder contents and rubber powder sizes on AAR were compared. The results indicate that the incorporation of scrap rubber powder can suppress the expansion of samples which caused by alkali aggregate reaction at the early age, and the inhibition rate of expansion can be more than 50%. The inhibition effect is weakened to 30% at the later age. The inhibition effect reaches ideal degree when the rubber content is 25%(by mass), its expansion inhibitory ratio can reach 35%. The growth of inhibition effect is not obvious with the increase of rubber powder content. Among the three different particle sizes of rubber, the 119μm has the best inhibition effect on AAR, but the improvement of inhibition is insignificant. The elastic scrap rubber powder with small particle sizes acts as concentration center of stress, they can reduce the emerging of crack effectively. The scrap rubber powder are hydrophobic, and they can induce air. Air bubble together with the scrap rubber powder plays a part in easing up the bulbs of pressure generated by AAR, then restricts the internal crack extension in cement mortar, and weakens the damage of AAR on the matrix.