Abstract: CORTH is a subchannel code self-reliant developed by Nuclear Power Institute of China（NPIC） based on four equation model with slip ratio to perform thermal-hydraulic analysis of reactor cores or experimental facility with heating rod bundles. The development of CORTH adopted modular design and object-oriented programming method, and specially provided with graphic user interface for input deck preparing and output analysis. CORTH has been executed software testing by independent third organization to ensure the readability and standardization of coding. Testing data in NPPs, international benchmark and AP1000 nominal condition were used to carry out verifications and validations of CORTH. The results show the good accuracy of CORTH that meets the requirement of engineering design and analysis.