With the development of the high voltage grid, it is the trend of the future power grid to unlock the electromagnetic loop network and to divide the grid. Grid division operation can effectively alleviate the phenomenon of complex grid structure and exceeded short-circuit current. A new method for power grid division based on Dijkstra algorithm is presented. Firstly, based on the knowledge of graph theory, the power network is transformed into the network topology, with the site and line impedance in the grid corresponding to the nodes and weights in the topology graph. Secondly, it finds the sites of which the shortest path from the initial site to the site within the specified range by Dijkstra algorithm. Taking 500 kV/220 kV power grid as an example, due to the development trend of the future power grid supplying high voltage level network with supporting role, the intervals are connected through the tie line, so 500 kV sites are selected as the initial station and some grid partition supported by 500 kV station can be determined. The proposed method can be calculated fast by programming without repeatedly solving. Finally, an IEEE30 node system and a practical power grid in a certain region are taken as examples, which demonstrates the effectiveness and practicability of the proposed method. This work is supported by Science and Technology Project of Guangdong Power Grid Limited Liability Company (No. 031900KK52160023).