Abstract: On the basis of RELAP5, COBRA-Ⅳ and NLSANMT codes, the three dimensional neutronics and thermal-hydraulics coupled system RECON was developed by means of the parallel processing model and parallel virtual machine technology. The ways of coupling were flexible since different combinations of codes can be selected for various coupled analyses. Validations of the coupled system were completed with a series of benchmarks. Specially in the MSLB benchmark, the comparison of results with other coupled codes demonstrates that RECON has good accuracy and is suitable for the analysis of reactivity insertion accident.