Abstract: In order to improve the safety and sustainability of a supercritical water-cooled reactor (SCWR) core, both sub-channel and MCNP analysis were carried out to assess thermal-hydraulic and neutronic performances of the fuel assembly, which was proposed for the fast zone of a mixed-spectrum SCWR (SCWR-M). This fast zone assembly had a multilayer structure and was axially divided into several seed and blanket regions. The effects of some design parameters, i.e. axial configuration, fuel rod diameter, pitch to diameter ratio and duct wall clearance on the thermal-hydraulic and neutronic performance of assemblies were investigated and an optimized parameter ranges were obtained.