The total energy of bcc Fe containing Cu clusters with different sizes and number densities are calculated using the molecular dynamics (MD) method.The results indicate that the Cu atoms prefer to form Cu clusters instead of being uniformly distributed in the bcc Fe matrix.The binding energy of substitutional Cu to Cu clusters is also found to increase with the number of Cu atoms.For a large-sized Cu precipitate,the change of the local stress state is found to relate to the phase transition from bcc to fcc Cu based on MD and common neighbor analysis.