Abstract: An investigation was made into the machanical properties under ambient and elevated temperatures of the P91 steel tubes produced by Chengdu Seamless Steel Tube Plant,The result shows that both temperature and stress impose tremendous influence upon high-temperature strength and sustained strength of the material. The home-made P91 steel tubes are in possession of proper high-temperature properties which are in compliance with those of tubes of the same kind made abroad. Also discussed in the paper is the said tube's low-cycle fatigue characteristics under ambient temperature.