Abstract: In simulation of ad hoc networks, the choice of underlying mobility models has a great influence on the network topology and performance of protocols. However, most of the existing mobility models that are designed for idealistic cases can not provide realistic movement scenarios. On the basis of RWP (Random Waypoint) mobility model, a novel realistic mobility model, RWP with entrances in the terrain (RWPWE), is proposed. In the proposed model, 1) There is at least one entrance on the edge of or in the terrain; 2) The movement pattern in a terrain can be described by RWP model; and 3) The node transfer from inside the terrain to outside through entrances is decided by the probability staying inside the terrain. The influence of entrances on the node mobility is characterized by the attributes of nodal velocity, transition time, transition length and spatial distribution in the terrain. Theoretical analysis and simulation show that due to the existence of terrain entrances the node mobility is more complex and nodal spatial distribution is greatly different from that of RWP model. Moreover, these differences have a significant impact on ad hoc network topology and the performance of protocols eventually.