Abstract: Under the conditions of ideal and shadow fading environments, with the assumption that nodes are uniformly distributed, the connectivity of mobile Ad hoc networks (MANET) is calculated in theory respectively. The exact formulas of connectivity, which shows the relation of connectivity, node number and node transmitted power, are derived its validity has been verified by the Matlab simulation. Then, network simulation model is constructed based upon OPNET and the network performances further demonstrate the rationality of the theoretical analysis.