Cognitive radio networks (CRNs) can make full use of spectrum resources of heterogeneous wireless architectures via dynamic spectrum access techniques. However, routing in CRNs impose challenges due to the fluctuating nature of the available spectrum. To study routing algorithm a model that can simulate CRNs routing protocol needs defining. Although Network Simulator 2(NS2) has been the dominate network simulation tool, it can't provide native support for CRNs routing simulation. In this paper, a new model named cognitive radio networks routing model (CRNRM) for Ad-hoc CR networks routing is proposed and deployed in NS2. Through simulation experiments, the feasibility of CRNRM is validated and typical routing protocol is evaluated.