Relating to plating of metal materials, the invention provides a preparation method of a titanium boride based inorganic composite coating. The mixed powder of micron-sized metal Al powder, micron-sized, submicron-sized or nano-sized TiO2 powder, and micron-sized, submicron-sized or nano-sized B4C powder is taken as a raw material, the mixed powder is sprayed on the alloy underlayer surface of a metal or alloy workpiece surface by thermal spraying. During thermal spraying, the Al, TiO2 and B4C in the mixed powder react with nitrogen in a powder feeding gas to synthesize the titanium boride based inorganic composite coating in situ. The method provided in the invention overcomes the defects of high raw material cost, complicated preparation process, high energy consumption, low efficiency, difficult control of coating processing precision, low coating density, poor coating uniformity, weak binding force between the coating and a substrate, low coating toughness, easy coating cracking, and unsuitability for application in large-scale industrial production existing in the prior art for preparation of titanium boride based composite coatings.