Abstract: By means of the optical microscope,scanning electron microscope and microhardness meter,the paper deals with the microstructure and property of a cost aluminum alloy after laser remelted treatment.The microstructure can be divided into remelted zone,transition layer and substrate.In the remelted zone,the width of dendritical pro eutectic α phase has been fined to 2～3μm from 20～40μm original state.Meanwhile the eutectic microstructure has also been broken up extremely.These changes make the microhardness of the treated surface be increased to 109～115μm from 67.4.