Titanium bearing blast furnace slag with 20%-30% titanium dioxide is a valuable second resource. The main problems to utilize the resource are the reduction of the titanium oxides,the separation of titanium and silicon and the second pollution. The main aim of the research is to prepare TiC by the united process of carbothermal reduction in vacuum and acid leaching based on the thermodynamics calculation. The results show that decreasing pressure of the system is helpful for the reduction of the titanium oxides. Titanium and silicon in slag can be separated completely. The second pollution decreases due to evaporation of Mg and SiO produced in vacuum condition. The optimum conditions for the united process to prepare TiC are slag size of 200 mesh, temperature of 1 673 K, and the mass ratio of slag to reductant of 100∶38.