Cognitive radio (CR) is a promising technology that enables opportunistic using of the unused spectrum to alleviate the spectrum scarcity problem. However, as the interference to licensed spectrum owners needs to be strictly controlled, CR enabled users (CRs) should vacate the using channel immediately on detecting licensed users activity and the end to end performance may be seriously degraded. In this paper, we propose a robust routing scheme for cognitive radio ad hoc networks that can accommodate to the spectrum availability variation and keep stable to guarantee the end to end performance of CRs. The path stability is modeled considering both available channel numbers and channel characteristic along the path. The paths beyond a robust threshold are regarded to be feasible and the one with maximal throughput is chosen for transmission. Simulation results show that the proposed scheme performs much better than other existing protocols in terms of route throughput and stability maintenance.