Transmission lines are vulnerable to impairment by a variety of disasters including high winds and ice cover, which pose a significant threat to energy security. At present, studies on wind and ice disasters on transmission lines are mostly focused on low-altitude areas.However, many west-east transmission lines cross vast plateau areas, in which long cross-bar transmission towers account for a larger proportion. In order to ensure the safe operation of transmission lines in high-altitude areas, this paper establishes a long cross-bar transmission tower-line system refined model relying on a ±800 kV UHV DC transmission project, based on the ice-covering conditions in high-altitude areas, ice-covered working conditions of transmission towers and transmission lines are established respectively. Concurrently, the wind load characteristics of high-altitude and low-altitude areas are compared and analyzed, taking into account the influence of environmental factors such as air density, topography and geomorphology in high-altitude areas. Finally, based on the ice-covering conditions and wind load characteristics in high-altitude areas, wind-induced vibration response analysis of the long cross-bar transmission tower-line system is carried out. The findings indicate that the wind profile at elevated altitudes is comparatively gentle, the displacement response at the cross-bar of the long cross-bar transmission tower-line system is more pronounced than that at the tower's summit, and the maximum displacement response of the structure under ice-wind loads occurs at the midpoint of the cross-bar end.