The low-altitude penetration technology of UAV capitalizes on environmental characteristics during real-time flight to mitigate the risk of attacks and enhance the likelihood of mission completion. Trajectory planning comprehensively consider environmental factors and aircraft performance to generate optimal trajectories. To address the challenge of generating low-altitude penetration trajectories in complex mountain environments, this paper proposes a method based on geographic feature extraction. This approach resolves issues such as slow trajectory planning and the complexity of environmental mathematical modeling across vast mountainous regions. By leveraging geographical feature information and extracting mountain valley lines as trajectory references, this paper employs the ESDF method and safe flight corridors for 3D trajectory planning. This geometric representation of complex flight environments enables the swift generation of UAV penetration trajectories meeting safety requirements. The trajectory planning method presented in this paper streamlines the planning process, boosts efficiency, and offers practical application value for UAV operations in mountainous terrain.