Four kinds of diameter scopes of RAP (reclaimed asphalt pavement),which were prepared to replace RBP (reclaimed base pavement) in the same diameter scope,were designed for the cement stabilized recycled mixture,in order to study the impact of old asphalt concrete on the performance of recycled mixture.The performances of the regeneration mixtures of skeleton dense gradation and suspended dense gradation were compared by indoor mechanics tests,and at the same time the electron microscope was used to observe the interface of the mixtures in which RBP was replaced by different partical sizes RAP.The results show that the strength and modulus of the regeneration mixture decreases and the drying shrinkage coefficient increases with the aggrandizement of the diameter of RAP substitution,when the RAP diameter is larger than 4.75 mm.The strength and modulus of the cement stabilized aggregate of skeleton dense gradation decrease slightly,while the dry shrinkage coefficient is obviously improved,when the diameter scope of RAP is 2.36~4.75 mm.The smaller the particle size of RAP,the easier the fusion at the interface between RAP and RBP.