During the implementation of the asynchronous interconnection of Yunnan Power Grid and the main grid of China Southern Power Grid (CSG), the system stability characteristics will change dramatically. In the implementation periods, power transmission section of Yunnan needs to be disconnected with different 500 kV AC tie lines, moreover, since the times of Luxi Back-to-back HVDC and Yongfu HVDC project being put into operation are uncertain, different asynchronous interconnection interim schemes have influence on the security and stability of the power system. In order to reduce the risk of system operation, this paper proposes interim operation modes for the implementation stage of the asynchronous interconnection projects and analyzes the corrsponding stability characteristics, with a focus on electric power system stability control system adaptability, configuration of the third line of defence, and engineering commissioning of Luxi Back-to-back HVDC and Yongfu HVDC projects, etc, effective suggestions are provided to improve the security and stability level of the power system.