The invention discloses a network reconfiguration preprocessing method and preprocessing system for reducing invalid solution in a power network, By simplifying the original grid, and defining the loop matrix, and then dividing and grouping the loop matrix, the method completes the preprocessing of the network reconfiguration, thereby avoiding searching in the infeasible solution, reducing the searching space, reducing the generation of invalid solution, improving the searching speed and saving the time cost. After the network reconfiguration preprocessing of the invention, the network reconfiguration speed can be effectively improved, and the economic operation purpose of the power network can be realized.