Ad hoc radio networks will play an important roll in the future mobile radio network due to its flexibility and low operation cost. However, because of the high randomness and complexity, most current research derived their conclusions based on simulation results and empiric analysis, lacking theoretical analysis of the ad hoc networks and their behavior. This paper presents a typical ad hoc network topology model and derives the statistic properties of neighbor nodes in such ad hoc networks. We also proposed approaches for theoretical analysis of ad hoc networks. At last simulation results are given to show the correctness of the model and our analysis. The main result derived from our investigation is that the average number of neighbor nodes is almost linearly proportional to the node density in the region being studied, while the node density has no influence over the average distance between neighbor nodes.