The invention provides a new method for preparing a TiN nanometer powder by adopting ammonia gas atmosphere heat treatment and using organic and inorganic mesoporous composites as precursors. Cheap hydrated titanium dioxide powder is used as the titanium source, and a liquid alkane mixture (C11-C16) is used as the carbon source, carbon coating is realized by stepwise gradual temperature rise and refluxing, and the precursors with mesoporous structure are prepared in virtue of volume contraction caused by the partial crystallization of titanic dioxide in the process of refluxing. The high-purity titanium nitride nano-powder is prepared by adopting ammonia gas atmosphere heat treatment with the precursors at a relatively low temperature (700 DEG C-900 DEG C). The titanium carbide powder prepared by the method is of spherical shape, has an average particle size of 20-40nm, and an average grain size of 10-20nm. The method has the advantages of simple technology, low cost and energy saving compared with the common preparation methods, and feasibility for large-scale industrial production.