Since it is difficult to determine the network boundaries and topology is very flexible in Wireless Mesh Network (WMN), topology information collection and reconstruction have great delay, so that real-time WMN monitoring accuracy can not be ensured. This paper proposed a real-time monitoring method based on improved A algorithm for the topology state of WMN to get the real-time state and give out response to abnormity. Through limiting the path length, reducing the search scope and adding the number of repeated searched edges to heuristic of A, the method solved the problem that path may be recovered and too long for topology real-time monitoring. The simulation results show that compared with the original algorithm, the improved algorithm has a higher speed in convergence, and it can update the topology construction in shorter time.