This work provides a promising approach to achieve the uniform distribution of TiCN nanoparticles (NPs) in aluminum matrix via a combination of ultrasonic dispersion and fast cooling processing. Microstructure analysis demonstrates that as the cooling rate is increased, the NP distribution in the matrix varies from intergranular to intragranular at micro scale and the NP-matrix interface from incoherent to coherent at nano scale. An analytical model is proposed to unveil the effects of cooling rates on the behavior of NPs at the solidification front. The theoretical analysis reveals that the NP size and cooling rate are the two prominent factors determining the NP distribution during solidification of nanocomposites. The experimental results yield an insight into the understanding of NP-induced microstructural evolution and shed new light on the development of high-performance nanocomposites.