This paper demonstrated that the strength and toughness of Al alloy could be improved when ultrasonic melt treatment， Sr/Ce complex modification and heat treatment worked together. The effect of solid solution treatment on the microstructure and properties of A356 alloy was also studied by metallographic microscope （OM），scanning electron microscope （SEM）， tensile machine and hardness instrument. The research results showed that melt treatment contributed to the improvement of the α-Al dendrites， and eutectic silicon phases， and the tensile strength of as-cast alloy reached 215MPa with elongation of 9.5%. After T6 heat treatment， the morphology of eutectic silicon changed from fibrous to spherical particles distributed independently， and mechanical properties were significantly also improved， except for elongation. As the solution time increased， the equivalent diameter of eutectic silicon decreased first and then increased， while the aspect ratio gradually decreased. Meanwhile， the tensile properties and microhardness of the alloys showed a trend of first increasing and then decreasing.When solution time was 4h， the optimized comprehensive mechanical properties of the alloy were obtained and its tensile strength，yield strength，elongation and microhardness reached 300MPa， 240MPa，8.0% and 110HV，respectively.