The invention discloses a titanium carbonitride blast furnace protecting agent and a preparation method thereof. The furnace protecting agent comprises the following components in percentage by weight: 50-74% of calcium carbonitride Ti (C, N), 17-40% of composition of CaO, MgO, SiO2 and AL2O3, greater than 1% of free carbon, greater than 3% of total iron TFe and less than 6% of titanium oxide. The preparation method comprises the following steps: selecting titanium concentrate, preparing carbon, mixing materials, forming, calcining, reducing, and carrying out carbonitriding of titanium, wherein the carbonitriding ratio of titanium is greater than 85%; the furnace wall at the corroded part of a furnace hearth is thinned, and the temperature of the corroded part is lower than the temperature of other regions, thereby forming a temperature gradient; and under the action of the temperature gradient, Ti(C, N) and attachments thereof are continuously accumulated and bonded in the corroded region until the temperature gradient relatively disappears. The invention overcomes the defects that in the prior art, the titanium content is unstable and the impurity content is high, the energy consumption is large, and the effective utilization ratio of titanium is lower than 30%; and the titanium carbonitride Ti (C, N) used as an effective component is directly formed in the molten iron of the furnace hearth and is deposited on the working surface of the corroded part of the furnace hearth or deposited in brick work joints to repair the corroded region, thereby performing the function of protecting the furnace hearth.