The refining and modification effect of Ti (from GRAI), B, Sr and RE (cerium-riched mixtures of rare earth) on the mechanical properties of A356 aluminum alloys under T5 and T6 treatment condition were studied by OM, SEM, EDAX, etc. It is found that the addition of RE to A356 alloys containing Ti and/or B and Sr makes strength and elongation increase in T6 treatment,but make elongation decrease in T5 treatment, at the same time, the long axis of α(Al) grain structure decreases and the mean diameters of silicon particles increase with RE additions increasing. Grain refining with 0.01%Ti plus 0.03% B makes the dendrite α(Al) grain structure transform into equiaxed structure, resulting in obvious increase of elongation percentage. The mean diameters of silicon particles in T5 treatment are smaller than that in T6 treatrnent. Roundness of silicon particles in T5 treatment is higher than that in T6 treatment. A356 alloys modified and refined with Ti, B and Sr obtain the best mechanical properties in T5 treatment,however, the alloys with Ti, B, RE and Sr additions obtain the best mechanical properties in T6 treatment.