The effects of microalloying elements, modification process of Si and heat treatment process on the microstructure and mechanical properties of Al-Si-Cu ternary eutectic alloy were studied by SEM, EDS and mechanical properties characterization. The results show that the θ phase distribution in the alloy is continuous when the Ni content is less than 0.1%, while the θ phase distribution in the alloy with the Ni content of 0.25% is obviously discontinuous. After modification, the Si in the alloy becomes vermicular, and the edges of the existing dendritic, flaky and primary Si also become smooth. The effect of θ on material plasticity can be further reduced by solution treatment. After θ phase distribution adjustment, Si modification, solid solution and 400 ℃ high temperature treatment, the elongation of the alloy increases by more than 8.5%.