Abstract: Based on sub-channel code COBRA-Ⅳ and neutron kinetics code NLSANMT, a three dimensional neutronics and thermal-hydraulic coupled code C4/NK was developed. In order to verify the coupled code, two typical reactivity initiated accidents (RIA): NEACRP control rod ejection benchmark and uncontrolled rods withdrawal benchmark at zero power, were calculated. The comparison of results with the reference solutions and other coupled codes shows that the C4/NK code has good accuracy and can correctly simulate the neutronics and thermal-hydraulic feedback phenomena during the transient.