Cooperation between UAVs can significantly improve overall positioning accuracy of unmanned aerial swarm, which is of great importance to swarm navigation. In complex terrain environment, positioning signals from navigation satellites and partner UAVs are often blocked, resulting in mixed presence of relative range and angle observation, causing serious reduction in positioning accuracy of some UAVs. In order to improve their positioning accuracy, this paper proposes a cooperative navigation enhancement method based on hybrid linearization belief propagation, which utilizes hybrid relative observations of range and range/angle between swarm UAVs. Simulation experiment is carried out in a complex-terrain environment based on 3D map to simulate signal blockage. Simulation result shows that the algorithm can utilize hybrid relative observations between swarm UAVs, has a good effect on the mitigation of inertial navigation position error, and is of great significance to navigation of swarm aircraft in GNSS-challenging environment.