The effect of alloy elements on the quasi-solid solidification behavior of Al-4.5Cu alloy has been studied. The results indicate that Si and La can reduce the hot cracking tendency of Al-4.5Cu; adding 2%Si to matrix, the releasement of crystallization enthalpies makes the recalescence very severe, so the alloy cracks and cant have high strength; Al4.5Cu3Si has a strong ability of compensation and its fracture stress is highest among the Al-Cu-Si alloys; adding of La can reduce the secondary dendrite arm spacing, and the hot cracking properties are improved obviously.