Security and stability control system (SSC) is an important guarantee for the safe operation of power grid, and for HVDC system modulation function is an important kind of stability control measures. Combined with Tianshengqiao-Guangzhou HVDC safety strategy transformation, RTDS simulation test is conducted. In allusion to the exposed defects about SSC handling with multiple DC power modulation orders and sequence coordination between SSC and pole control system, the processing means for the stability control device of Mawo converter station and control characteristics of DC power downhill for pole control system are analyzed in detail. An optimization method of control sequence coordination for stability control system and pole control system is proposed and tested on the SSC test platform. Test results show the effectiveness of the proposed method, and this method can provide guidance for the design and implementation of SSC scheme of HVDC project with similar techniques.