Abstract: To solve the problem of insufficient neutron moderation of the super critical water-cooled reactor (SCWR), the water rod or the adding of the solid moderator is commonly used in assemblies, and a multi-pass flow scheme is adopted, which resulting in the complication of the fuel assembly and the core structure, and the strong neutron absorbing materials are introduced into the reactors. Based on the result of CSR1000 study, the simplification of assembly and core structure was carried out. The results significantly simplified the assembly and core structure of SCWR.