Abstract: The high-fidelity multi-physics coupling platform can be established through coupling Monte Carlo neutron transport code MCNP5 and commercial CFD software STAR-CCM+. A coupling code written in Perl language was employed to couple MCNP5 and STAR-CCM+ by ASCⅡ text data files. For fuel and moderator cells which have strong feedback effects, the hexahedral mesh model option “trimmer” of STAR-CCM+ was chosen to realize a one-to-one correspondence with MCNP5. For cladding cells which have weak feedback effects, the volume weight method was adopted. The steady-state high-fidelity neutronics and thermal-hydraulics coupling code was developed under Linux platform. The single fuel element and 3×3 PWR lattice model were calculated using the coupled code. The numerical results demonstrate that the method and model proposed in this paper are applicable for high-fidelity neutronics and thermal-hydraulics coupling calculation.