Low frequency oscillation online analysis will obtain a number of oscillation modes. Dispatching operators need to distinguish typical oscillation modes and take actions to improve mode damping in emergency state based on mode type and relevant zone. A method based on electrical distance between operating districts is proposed to identify relevant zone and mode type, operating districts of power grid are determined through topological analysis, representative bus with highest voltage level is selected for each operating district. Buses with higher participation factor are chosen as strong correlative buses and divided into two clusters according to the angle of mode shape. Each cluster will be associated with the operating districts corresponding to strong correlative buses. Electrical distance of representative buses is calculated by multi-port equivalence. Relevant zones of two clusters are obtained by aggravating operating districts with smaller electrical distance. Local oscillation mode and inter-area oscillation mode can be discriminated based on electrical distance between operating districts with buses of largest participation factor in each cluster. The effectiveness of the method has been verified by the cases of actual power grid. This work is supported by China Postdoctoral Science Foundation (No. 2016M591738) and Postdoctoral Science and Research Program of Jiangsu Province (No. 1601160C).