Abstract: Monte Carlo is a statistical method widely used in solving particle transport problems. A Monte Carlo code has the advantages of much flexible geometry and high fidelity. Taking advantage of this, reactor core analysis can be solved with high fidelity, although much computing cost is needed. With the feedback of a thermal hydraulic code, the core in hot full power condition on steady state can be computed by a Monte Carlo code. In this paper, JMCT, a Monte Carlo code, and COBRA-EN, a subchannel code, are coupled through the method of internal coupling. Picard iteration is used between neutron transport calculation and thermal-hydraulic calculation. The HFP steady-state calculation in a mini-core benchmark in NURISP project is used to validate the coupling code. The result agrees with that of SERPENT2/SUBCHANFLOW and TRIPOLI/SUBCHANFLOW, verifying the accuracy of this code.