Moving the path of the beacon has an important impact on the localization performance in a wireless sensor network with mobile beacons; however, without full consideration of the influences of the distribution and density unknown nodes’ when planning beacon’s moving path, most of existing localization methods have lower efficiency. In this paper, the beacon model is first presented according to the theory of equal distance 3-optimal-coverage. Next, a heuristic path planning method is proposed for the ROI in which unknown nodes are distributed randomly, and the node density is limited by using the location mechanism of RSSI to locate range-free, unknown nodes. Simulation results show that the given method is effective.