The invention relates to a wireless sensing network node positioning method based on an optimal beacon set, which comprises the following steps of: 1, establishing a wireless sensor network comprising beacon nodes assisting for positioning and a target node to be positioned; 2, when an unknown node moves, updating the position of the unknown node and sending a positioning request packet, and whenthe beacon nodes receive the positioning request packet, sending an information packet comprising the node and the position coordinates; 3, after the unknown node receives the information packet of the beacon nodes, sequencing the beacon nodes from big to small according to an RSSI value, and establishing the mapping of a distance from the RSSI and the unknown node to the beacon node; 4, selecting four nodes nearest the unknown node from the beacon node set, wherein each three beacon nodes form a set of beacon set, and one set with minimum collinearity is the optimal beacon set; and 5, obtaining the initial position of the unknown node by adopting a maximum likelihood method. The invention has the advantages of low complexity of algorithm, little communication overhead among the nodes andhigh positioning precision.