Ultrafine TiN powders were synthesized by Carbothermal Reduction-Nitridation (CRN) method using nano titania and nano carbon black as raw materials. Phase transition sequences during reaction and influence of main technological factors were investigated using X-ray diffraction (XRD), thermogravimetric analysis (TGA) and scanning electron microscope (SEM). The results indicate that phase transition sequences were TiO2 up arrow Ti10O19 -> Ti3O5 -> TiOxNy -> TiN. At the same time, CRN reaction consists of three continuous stages. In the first stage, nano TiO2 powders were reduced to Ti3O5. In the second stage, Ti3O5 was totally converted into TiOxNy. TiN solid solution formed completely by the end of the third stage. The rapidest reaction rate was observed in the second stage and the lowest was in the third stage. Higher reaction temperature, longer isothermal time, or larger nitrogen pressure was in favor of synthesizing TiN powders.