Abstract: The segregation characteristics of Ni, Mn, P and C atoms at the phase boundaries of AlN/α-Fe matrix, Cu-rich precipitate/α-Fe matrix and AlN/Cu-rich precipitate in reactor pressure vessel (RPV) model steel were investigated by atom probe tomography (APT). RPV model steel specimens were heat treated at 890℃ for 0.5 h followed by water quenching and aging at 500℃ for 20 h. The results demonstrate that Ni, Mn, C and P atoms do not segregate to the Cu-rich phase/AlN phase boundary, only segregate to the AlN/α-Fe and Cu-rich nanophase/α-Fe phase boundaries, and their segregation characteristics have no significant differences. It is also observed that Mn has a larger segregation tendency than Ni, and C has a larger than P at both different phase boundaries of Cu-rich nanophase/α-Fe and AlN/α-Fe.