Abstract: The reactor core is the coupled result of the multi-physics including the neutronics, thermal-hydraulics, fuel and so on. Coupling the advanced nodal core key program NACK V1.0, core thermal-hydraulic analysis program CORTH V2.0 and fuel rod performance analysis code FUPAC V1.1, the reactor core steady simulation system CSSS V1.0 was got. CSSS V1.0 was used to simulate typical pressurized water reactor core. The calculation result of pressurized water reactor benchmark problem NEACRP-L-335 shows that CSSS V1.0 is in good agreement with benchmark program PARCS.