The ultra supercritical unit with the high temperature parameters and the large capacity has been developed in order to achieve the high efficiency of thermal power units and the clean energy use. However, the steam temperature and pressure of thermal power units have been further increased, which present more stringent requirements for the material performance. This paper summarized the selection approach of heat resistant steel for the different parts in ultra supercritical units, as well as the existing problems in the using process of heat resistant steels. Furthermore, the development tendency and the material requirements were reviewed for 700 ℃ultra supercritical units.