Abstract: Large-break accident analysis of China Super-critical water-cooled Reactor with the related electirc power of 1000 MW（CSR1000） were carried out using APROS code to clarify its characteristics and to evaluate the capability of its safety system.At the cold-leg large-break,the reverse-flow in the core happens immediately due to the blowdown of coolant at the break.The reverse-flow drives the high temperature and low density fluid into the core,which results in the heat transfer deterioration in the core and the cladding temperature increasing quickly.After the opening of ADS valves,the positive-flow in the core has been covered,and the excessive core heat-up has been mitigated.The high feedwater tank can provide the coolant supply at the early period;therefore,the low pressure injection system gets more time to be actuated.After the blowdown phase,the core has been re-flooded gradually by low pressure safety injection system.The maximum cladding temperature of large break accident is lower than the criterion（1260℃） by about 340℃,which appears during the blowdown phase.