Abstract: A new concept of SCWR was studied, including closed square fuel assembly with double-row rods, low-leakage core of pressure vessel type reactor, passive safety system, reactor control system, sliding-pressure start-up scheme, steam circulation system, etc. The analyses of coupled neutronics and thermal-hydraulics, sub-channel, typical accidents, control system, system stability and start-up process were carried out. The calculating results show that the major design of the core and system fulfils the design criteria, and the SCWR design concept is balanced and feasible.