Structural changes of three molten CuN（N=57,58,59） clusters during freezing and two Cu55 clusters with perfect icosahedral geometries in the coalescence processing at 300 K are investigated by molecular dynamics simulations based on the embedded atom method. Simulation results show that both freezing and coalescing processes have distinct stages. There exist great differences in atomic movement and microstructure change among the three CuN（N=57,58,59） clusters during freezing, which result in the different patterns of atomic packing in the three clusters. Of the three clusters, the ordered degree of the Cu59 cluster is the lowest. Initially structural changes of the two Cu55 cluster during coalescence result from large position displacements of atoms due to the deformation, then the atomic diffusion plays a mainly role in changing structure. The atoms far from the contact region between the two clusters can remain their origin structures.