Abstract: Carbon nanotubes reinforced aluminum matrix composites were prepared by friction stir processing. The effect of remelting temperature,remelting times and cooling mode on microstructure of composites was investigated. The experimental results showed that the grain boundary precipitate of composite significantly increased compared with matrix alloy due to the intervention of CNTs. With the increasing CNTs content,the grains are refined gradually,and the enrichment of CNTs were aggregated in the grain boundary position. composite material grain obviously coarsening after remelting. When the remelting temperature is 800℃,the(α) Al dendrite is uniform and fine; When the remelting times is 5 times,both dendrite(α) Al phase and Al-Si eutectic became fine and well-distributed.