Abstract: Aluminum alloy 7050 large scale billets were prepared with 300、1 000 W ultrasonic field and without ultrasonic field in semi-continuous casting respectively. The second phase morphology of different ingot was observed, and the content of solute elements was analyzed. The results indicate that the non-equilibrium eutectic organization becomes small and scattered in the ingot with ultrasonic. The composition curves of Zn, Mg and Cu with ultrasonic field become gentle compared with conventional ingot and the effect is more obvious with 1 000 W ultrasonic. The relative intracrystalline solubility of Zn, Mg and Cu increases respectively by 6.36%, 19.44% and 10.14%,and the parameter k_e becomes larger with ultrasonic field and increases significantly between 0.04~0.24 in the early solidification. The microsegregation in the edge and central portion of the ingot cross-section are effectively weakened with 1 000 W ultrasonic field, and the effect is relatively poor in 1/2 part from the center to the edge. Because the cooling rate at the solidification front is promoted by 1 000 W ultrasonic field, and there are more solute elements in α-Al, the microsegregation of each element in the ingot is alleviated.