When the grid structure area of county power grid is weak, its fragility is exposed in the face of major natural disasters (such as typhoon), which would result in serious consequences such as power loss in the whole city. If the traditional small hydropower resources of regional county power grids are abundant, by carrying out the regional multi-operation mode control and constructing the dispatching assistant decision-making system, the regional power grid can also continue to supply important load in the face of major natural disasters. In this paper, in terms of a county-level power grid characteristics, the operation and control technology of the fragile county-level rural power grids under the risk model is studied to construct the demonstration project, improve the ability of resisting the risk of regional power grid and ensure the important load of county power supply. The effectiveness of the decision system is verified by simulation analysis in the actual power grid.