In this paper, the authors present a Visible Obstacle Mobility model Based on Activity Area (VOMBAA) for ad hoc network. Typical examples where the nodes of mobile ad hoc network are human-operated are natural or man-made disasters, military activities and so on. In these scenarios, people don't move random and their sights are obstructed by obstacles. In the proposed mobility model, nodes are divided into several clusters. Each cluster has properties of activity area, speed, pause time and capacity. According to different clusters, the corresponding nodes' activity areas are also different. There are no existed roads in this model, the nodes move around the obstacles in a natural and realistic way.