Abstract: A coupled neutronic and thermal-hydraulic code system CASIR（Core Analysis System for Innovation Reactor） for SCWR core steady state is developed due to the rapid variation of coolant density along the axial section in SCWR（supercritical water cooled reactor） core.The code system consists of the improved neutronic codes which are used for PWR（pressurized-water reactor） neutronic calculation and the sub-channel thermal-hydraulic code which is applicable for SCWR fuel assembly calculation,including the function of adjusting the flow rate distribution in the lower plenum of core.The coupled code system is tested on a two pass SCWR core of first cycle in the beginning of cycle by comparing the results with those calculated by Monte Carlo code,and it shows that the CASIR system is applicable to simulate the SCWR core preliminarily;main results of burn-up simulation are obtained by adjusting the core flow distribution in order to restrict the maximum cladding-surface temperature below the limit of design.All above show that the CASIR code system satisfies the requirements of SCWR core design and can be used for conceptual design of SCWR core with square assemblies.