Abstract: In received signal strength indication (RSSI)-based positioning, the deployment structure of beacon nodes greatly affects the accuracy of positioning. In theory, the intensive and well-proportioned distribution of these deployed can insure the high precise positioning results. However, the RSSI is seriously disturbed by noise in the actual environment, which makes it difficult to ensure stable signal propagation even if the layout is reasonable. In addition, dense deployment can lead to crosstalk between signals, and complex physical environments make it difficult to achieve ideal deployment of beacon nodes, which greatly affects the positioning result. In this paper, we propose an algorithm for optimal selection of beacon nodes in trilateration positioning. After beacon deployment, the optimal reference beacon combination for each local region in the positioning scene is constructed according to the geometric relationship of the beacon nodes. Then, the beacon sequence scanned by the device in real time is matched with the regional best beacon combination. The preferred beacon nodes are used to solve the position, and the positioning accuracy is improved by optimally selecting the reference beacon nodes. Experiments show that the proposed algorithm can improve the positioning accuracy efficiently, which is close to the result of selecting the best reference beacons.