As the limited radial geometry scale, the pressurized small reactors have strong neutron leakage. Consequently, it is difficult to obtain accurate results for a deterministic code with assembly-wise-homogenization scheme. Meanwhile, in the nuclear design of small reactors, large amount of gadolinium burnable poisons is adopted to control the core power distribution during the fuel depletion. This is also the motivation for the detailed burnup calculation. Monte Carlo method can be used as the reference due to the characteristics of continuous energy and geometry adaption. The reactor-oriented Monte Carlo code, RMC, can perform a full-core fuel cycle computation by coupling with the thermal–hydraulic calculation and the depletion calculation. This code model is validated by measurements of commercial reactors firstly, and then is applied to a small reactor design. Some neutronics parameters of the first-cycle of the small reactor are given by the coupling analysis with full-core detailed model. These results are also be used as the reference for the nuclear design code, PCM. The comparison shows that the calculation accurate of PCM is acceptable.