Abstract: The current situation and existing problems of security and stability control system（SSCS）of ultra-high voltage direct current（UHVDC）transmission are analyzed in the aspects of the system architecture,the interface between SSCS and pole control and protection system（PCP）,failure criterion of converter devices and control strategies of the grid.The engineering experience of UHVDC SSCS projects in China is summed up,the standard design schemes are proposed.The research focuses on the interface and communication protocol between SSCS and PCP,fault criterion,UHVDC power loss algorithmic,and coordination of security stability control strategies.The design scheme proposed has been applied in FulongFengxian,Jinping-Suzhou,and Yibin-Jinhua UHVDC transmission projects.Also,the study has great significance for other designs,development and implementation of UHVDC SSCS.