This paper introduces the hierarchical structure for the control and protection system, describes the control and protection system interface scheme in Qing’ao station of Nan’ao multi-terminal HVDC flexible project. Through the analysis of reactive power step and total DC harmonic on DC side in Qing’ao station, it proves the interfaces among valve group control, valve control and valve to meet the requirements of control and protection system. The scheme is simple, reliable and easy to realize, and has been successfully applied in Nan’ao HVDC project which greatly meets the requirements of the control and protection system in rapidity and reliability.