An automatic loop unwrapping method for electromagnetic loop network is proposed in this paper. Firstly, the electrical distance matrix is used to pre-splitting the power grid, and then the improved coherent algorithm based on the complex network weighted modularity proposed is used to condense the pre-split partitions and get the solution finally. The denominator operation mode of 500 kV substation is considered. The power supply mode with two to three 500 kV substations as the core is formed in each partition of the obtained solution, which limits the main transformer capacity of each zone, thus limiting the short-circuit current in the zone and improving the security of grid. The proposed electromagnetic ring network unwinding method is applied to a regional power grid, and the results show that the method is effective. This work is supported by National High-tech R & D Program of China (863 Program) (No. 2015 AA050101).