Abstract: This paper established an alternative interaction analysis method, i.e. the path series expansion method, for power systems with multiple devices. Based on this interaction analysis method, an intuitive relationship between each device itself as well as the interaction paths among them and the system stability was explicitly depicted. It also helps to understand the physical mechanism behind the system stable/unstable phenomena. Further, the path series expansion method quantifies the contribution of multiple subsystems (i.e., each device itself as well as the interaction paths among them) on the system stability, which remedies the deficiency of frequency domain analysis methods that were tailored for only two subsystems. Finally, based on a scenario with three kinds of typical devices, and the IEEE power system with 16 machines, the detail derivations, theoretical analysis and time-domain simulation on case studies were presented. Their results validate the effectiveness of this method.