IEEE802.16 standard provides interface protocol of wireless access system for physical (PHY) layer and Medium Access Control (MAC) layer. It supports two kinds of network topology: Point to Multi-point (PMP) and Mesh. This paper descries the MESH model characteristics and how MESH Model was supported in MAC layer by introducing full process of new nodes in Mesh mode accessing network. Furthermore, On the basis of comparing PMP model and MESH mode in MAC-layer structure, function and requirements, it comes to the conclusion: MESH nodes can access network faster and cost less than PMP nodes. Which makes it possible for those areas far away from center base station to establish multi-hop network with less investment and time cost, while coverage is expanded.