Abstract: During the pre-conceptual design of supercritical water-cooled reactor (SCWR), assembly design is very important and affects core performance. Coupled neutronics and thermal-hydraulics analysis is required for dramatic changes of water density in SCWR. Annular fuel assembly was optimized from the point of view of neutronics and thermal-hydraulics performance using three-dimensional coupling code. Three-dimensional diffusion calculation for annular fuel assemblies was carried out using FENNEL-N and pin power distributions were obtained. With these pin power distributions, SUBSC was used to perform the subchannel analysis. The effects of fuel rod distance and gap between fuel rods and assembly box on assembly performance were researched in the coupled analysis. Results show that increasing fuel rod distance and rod-to-box gap will increase k_inf and assembly power peaking factor. It is also shown in the results that heating heterogeneity of sub-channels plays a big role in assembly thermal performance and adding grid will flatten coolant outlet temperature as well as decrease maximum cladding surface temperature. Safety analysis of annular fuel assembly shows that the assembly is safe from the point of view of neutronics.