To investigate the influence of tantalum content on high-temperature mechanical properties of low-carbon reduced activation ferritic/martensitic (RAFM) steels,RAFM steels containing different tantalum contents (0 and 0.073％) were fabricated,and the tensile tests at room temperature and high temperature were performed,as well as the creep tests were conducted at 550 ℃ with the applied stress of 180 and 220 MPa.It was found that 0.073％ tantalum addition results in the increase in amount of stable carbonitrides (MX),and the creep rupture time of the steel under 180 MPa is obviously increased.In addition,the increase in MX caused by tantalum addition also leads to the improvement of high-temperature tensile strength.The improvement of high-temperature mechanical properties of RAFM steels is primarily related to the evolution of precipitates.