In order to preliminarily investigate the feasibility of nickel electroplated Co-pellets working in non-neutron irradiated steady state pressurized water reactor and influence of extreme accident on electroplated nickel coating, the nickel plated Co-pellets are heat treated at 400 °C, 600 °C in 2 MPa helium environment for 240 h, 0.5 h, respectively. The surface and fracture morphology of the electroplating nickel layer are characterized by scanning electron microscope. The diffusion of interface elements between coating and substrate is analyzed with energy dispersive spectrometer. Results show that the abrupt change of thermal expansion coefficient near Curie temperature 358 °C of nickel layer and the phase transition of cobalt near 427 °C will not cause destructive damage to nickel coating. The element inter-diffusion of interface makes the combining of coating and substrate more closely.