The invention provides carbon-doped nanometer titanium dioxide and a preparation method thereof and belongs to the technical field of nanometer materials. According to the carbon-doped nanometer titanium dioxide and the preparation method, the problems of the conventional carbon-doped nanometer titanium dioxide that the preparation process is relatively complex, the environment is polluted, the cost is high, products are different in particle size, and doped material is not uniformly distributed can be solved. A powder pulping method provided by the invention comprises the steps of mixing a titanium source with combustible organic matters and carrying out incomplete combustion. According to the carbon-doped nanometer titanium dioxide and the preparation method thereof, the combustible organic matters and the titanium source are ignited after being mixed, and a carbon-doped TiO2 nanometer material can be obtained due to the incomplete combustion of the organic matters and has the advantages that the process is simple, the pollution is avoided, the cost is low, the particle sizes of the products are uniform, and the doped materials are uniformly distributed.