Abstract: Two types of missing judgment problems currently exist in topological observability analysis based on the solvability condition of power flow.Based on the fact that there can only be one unknown state voltage parameter in one measurement island,this paper presented a method of adjacency table of boundary nodes with injection measurement that can systematically analyze and observe these missing judgment problems.The first type of missing judgment,which indicated that even the overall network was not mergeable,yet the partial network could be combined,was settled by using combination of local equations solvability and heuristic search algorithm.After analyzing the conditions and requirements of two networks with intersection that could be judged together,this paper solved the second type of missing judgment that the power flow of two unsolvable networks was solvable when combined.A 15-node case and an actual grid example were used to test the validity of the method.