A mobile ad hoc network (MANET) is a collection of wireless mobile nodes communicating with each other using multi-hop wireless links without any existing network infrastructure or centralized administration. In recent years, a variety of routing protocols targeted specifically at this environment have been developed and some performance simulations are made. However, the related works took the simulation model with a constant network size and a varying pause times or mobility velocities. And these works do not take into account the influence on the protocols when the mobile nodes’ pause time is invariable but the network size is changing. On the contrary, This paper considers the problem from a different perspective, using the simulation model with a dynamic network size and an invariable pause time which should be zero under weakest case because a longer pause time of the node may be insignificant for mobile Ad hoc network with frequently and fast moving nodes. Furthermore, based on the QoS (delay, jitter, throughput, loss ratio), routing load and the connectivity (to our knowledge, we first use the jitter and the connectivity as the valued metrics in the simulation of wireless ad hoc network protocols), this paper systematically discuses the performance evaluation and comparison of four typical routing protocols of ad hoc networks with the different simulation model and metrics, and drew more complete and valuable conclusions.