Abstract: The reactor core phenomena can be simulated and predicted with the high-fidelity neutronics coupled with thermal-hydraulics analysis, and the economic and safety of nuclear reactor could be further improved by using this new simulation tools. This work studied the methods of precise geometry modeling, accurate neutronics calculations and coupling with the pin-by-pin subchannel thermal-hydraulics, and a new high-fidelity neutronics and thermal hydraulics coupling code ENCP-X/CTF are developed. Some sensitivity analysis of the fuel rod heat conductance model, gap conductance model to the coupling results is performed, and the coupling system is applied for the large pressurized-water reactors. The results demonstrate that not only accurate macro parameters could be obtained, but also the detailed pin-level power distribution and temperature distribution could be analyzed.