Particle-reinforced Al-Si composites exhibit excellent mechanical and thermal properties, making them suitable for aerospace and automotive applications. However, in situ synthesized nanoparticle-strengthened Al-Si alloys often face challenges such as particle clustering and the formation of defects such as pores and inclusions during fabrication and processing, which significantly deteriorate material performance. Consequently, methods for improving particle distribution and melt purification are urgently needed. On this basis, the influence of remelting combined with ultrasonic vibration on the microstructure and flexural strength of 2 wt.% TiB2/Al-Si composites was investigated. The results demonstrate that the introduction of high-energy ultrasonic vibration during remelting effectively breaks out particle agglomerations and enhances the uniform distribution of nanoparticles. Additionally, remelting suppresses the coarsening of primary Si, reducing its average size by 18.8% after remelting at 750 ℃ compared with the as-cast state. The flexural strength of the TiB2/Al-20Si composite reaches 304 MPa, representing a 14.6% improvement over that of the nonremelted material. The thermal conductivity of the TiB2/Al-20Si composite reaches 169.4 W/(m·K), representing a 4.8% increase compared with its state before remelting.