Abstract: The state of the reactor system is closely related to core physics, fluid, structure,control and external conditions. In order to fully consider the multi-scale and multi-physical coupling characteristicsof the reactor, it is necessary to establish the system-level coupling analysis software to evaluate the behavior characteristics of the reactor system under steady-state, transient and accident conditions. The unified interface ICoCo（Interface for Code Coupling） has the advantages for reuse. Based on ICoCo, this paper encapsulates system code Relap5mod3.2, and then schedules Relap5mod3.2 by supervisor flow control scheme, regression tests were carried out to verify that the calculation results are consistent before and after the encapsulate. On this basis, the ICoCo interface input and output interface related data of nozzles, control bodies, pumps and valves and other important components are developed, on the one hand, the concurrent coupling of two Relap5 code is carried out to verify the correctness of the coupling interface, on the other hand, by moving the control module outward. Relap5 is controlled in the supervisor, which allows more advanced control and optimization algorithms to be applied to the design, analysis and optimization of reactor control safety system in the future.