With an explosive growth of wireless sensor networks (WSN), many of their features and applications have become important. Localization of sensor nodes is one of the most important problems in WSN whose accuracy has a very large impact on its performance. Global positioning system (GPS) is a well-known and powerful way which differentiates methods of its use on each node individually. But, because of high energy consuming and processing GPS, it is inappropriate for WSNs. Different algorithms are suggested to overcome the consumed cost of GPS by putting GPS on only some nodes instead of all nodes in the network for localization. So, for nodes localization, just a number of nodes exploit GPS and, they can help other nodes of network in localization via distribution of their coordinates. The use of a mobile robot to send signals to coordinate the target node localization is a good idea. The mobile robot should move in the right path and can localize node more accurately at lower cost. This paper proposes a new method to localize all nodes through some localized nodes based on graph theory in a tree and network topology. The proposed method provides better performance at the cost of accuracy and the number of nodes that can be made up of local consumption.