To study a backup navigation scheme for allowing temporally GPS faults or degradations, a natural-landmark scene matching visual navigation method based on dynamic keyframe is proposed for Unmanned Aerial Vehicle(UAV).Firstly, this method could autonomously describe and check featured natural landmarks by analyzing image sequence from on-board camera. After abstraction of keyframes including featured natural landmark, UAV will be located by the means of NLSM (Natural-Landmark Scene Matching) based on dynamic keyframe. Additionally, this navigation scheme adopts interframe scene matching algorithm in order to improve the navigation performance of accuracy, reliability and runtime. Experiments show that the backup navigation scheme proposed meets the requirements of navigation in complex and unknown environment for UAV.