Abstract: As examples of the power system widespread blackout accidents occurred in China and abroad,the failure risk of the traditional measures of three-defense lines for power system security and stability were analyzed in this paper.And a super defense line to prevent the loss of stability and widespread blackout of power systems was proposed,that is,the response-based wide area control（RWAC） for power system security and stability.The framework of RWAC,the key technology of RWAC and the new research progress of RWAC were presented in the paper.