Abstract: The 20Cr-25Ni austenitic steel used for super high critical pressure boilers must have high creep rupture strength under high temperature and high pressure. The paper studied the influence of additions of Nb, Ti and C on creep rupture strength of 20Cr-25Ni austenitic steel and metallographic structures of the steel with such contents, and it also analysed the optimum contents of Nb, Ti anb C.