An ad hoc network is a collection of wireless mobile nodes dynamically forming a temporary network without using any existing network infrastructure or centralized administration. Because of its acentric, self-organized, fast deployable and mobile property, people are paying more attention to the using of ad hoc network in the emergency. In such an environment, multiple networks "hops" may be needed for one node to exchange data with another across the network, due to the limited range of each mobile node’s wireless transmissions. So for an ad hoc network, a rational routing protocol is especially important. The paper will analyze the character of ad hoc network and the special requirement for communication protocols. Toward the routing protocols, this paper presents four multi-hop wireless ad hoc network routing protocols that cover a range of design choices: DSDV (Destination Sequenced Distance Vector), TORA (Temporally Ordered Routing Algorithm), DSR (Dynamic Source Routing), and AODV (Ad hoc On-demand Distance Vector). After thoroughly analyzed the network structure and routing protocols, the paper gives the proposal of a new hybrid routing protocol and the view for future work.