IEEE 802.15.5 standard supports mesh networking for IEEE 802.15.4 based low-rate wireless sensor network (WSN). Through assigning a consecutive address block (CAB) to a node, IEEE 802.15.5 enables routing without table, which eliminates route discovery latency and reduces communication overhead and energy consumption in addition to saving storage space for routing table. With CAB, however, a node may fail in joining the mesh network due to insufficient address. To overcome the address-lacking problem, the scheme called Borrowing Address from Two-hop Neighbor (BATN) is proposed in this paper, which provides with two procedures for the nodes to join or leave the mesh, respectively. In addition, the routing scheme under BATN is presented. Both theoretical and simulation results show that the proposed BATN is better than the basic address assignment scheme introduced in IEEE 802.15.5 standard and the existing address borrowing schemes in terms of the probability of the node's successful joining the mesh network and the number of bytes used in reporting the number of children in address assigning stage.