Fenghuoshan tunnel on Qinghai～Tibet railway, with an altitude of 4900 meters, is at present the highest railway tunnel in the world. The natural conditions, such as the extremely coldness and oxygen deficiency, impose great difficulty for the construction of Fenghuoshan tunnel. On basis of presenting the construction methods of Fenghuoshan tunnel, the author summarizes the specific solutions for the excavation, lining, concrete construction, waterproofing and drainage, ventilation and exhaust air control and freezing prevention and thermal keeping of tunnels under extremely cold and oxygendeficient conditions, which can provide reference for similar works in the future.