An integrated scheme of emergency DC power support which is based on dominant center of Inertia DCOI is proposed to improve power system transient stability. The inter-area speed differences equivalent by dominant center of inertia alleviates the main weakness of the traditional signal which is made of the frequencies at both sides and is represent of abnormal information of the nonlinear dynamic behavior of the power system based on a model in which two AC systems are connected by a HVDC Link. Sichuan Power Grid connected with Southwest Power Grid by Deyang-Baoji HVDC project is used to testify the method. The simulation results show that the control strategy can significantly advance the transient stability of AC/DC system through extended equal area criterion (EEAC).