Two vertical sections of the Fe-C-Ta system with 0.1wt.%，0.5wt.% ta were experimentally investigated by DTA, and the phase transformation sequences of the alloys Fe-2.93C-0.1Ta and Fe-2.31C-0.5Ta were analyzed. A thermodynamic calculation of this system was carried out using CALPHAD technique. The results show that the thermodynamically calculated results agree well with the experimental data. There are four nonvariant reactions in the liquidus projection of Fe-C-Ta system in the Fe-rich corner: Liquid bcc ?fcc TaC，Liquid ? bcc Fe2Ta TaC，Liquid ? Fe3C TaC fcc，Liquid Ta2C ? TaC Fe2Ta. The temperature of the nonvariant reactions is as following: 1443.26℃, 1413.90 ℃,1122.42 ℃, 1508.64℃.The eutectoid reaction occurred at 726.6℃of the alloys Fe-2.93C-0.1Ta and Fe-2.31C-0.5Ta.