Nano TiN-Al2O3 composite powders were prepared by in-situ nitridation using nano TiO2-Al2O3 powders prepared by a coprecipitation method as starting material. The nitridation conditions and mechanism were calculated and analyzed by using thermodynamic principle. The effect of nitridation reaction conditions on nitridation reaction was studied. Experimental results show that the nitridation reaction begins at 700°C and completes at 900°C for 5 h. TEM micrographs show that nano TiN particles are dispersed into Al2O3 matrix. The size of nano TiN particles is about 50-70 nm.