Regarding the important role of grid structure and electrical distance in power grid division, a fast selection method of power grid division node based on ripple diffusion mechanism is proposed According to the characteristic that the high voltage substation is selected as the central point in the grid division and the principle that ripples first arrive at the shortest distance from the central source when they diffuse outward, .firstly, the power network is transformed into a topological graph. Then, by simulating the ripple diffusion process, the points whose shortest path from the source node within the prescribed distance will be searched, and these nodes are partitioned into the same partition with the source node. Finally, taking 500 kV/220 kV power grid as an example, the 500 kV site is selected as the initial source node, and the grid division with the support of the 500 kV site is determined. The accuracy and practicability of the proposed method are verified by the IEEE39 node system and the actual power grid in East China.