This paper concerns an efficient network joining method for mobile nodes in USNs (ubiquitous sensor networks) based on the IEEE 802.15.4 standard. The MSBS (mobile sensor beacon setup) method is proposed for performance enhancements of the mobile nodes using the depth, traffic, and RSSI (received signal strength indication) information. The MSBS method can transfer trusted data and prevent traffic overloads at specific nodes. For the performance analysis, the information from the mobile nodes in USNs is investigated and analyzed using the proposed method. Simulation results show that the MSBS method provides an efficient network joining according to the mobility of nodes in USNs.