By utilizing the high-temperature chemical reaction between Ti and AlN, TiN reinforced titanium matrix composite coating is in-situ synthesized on TC4 alloy substrate by laser cladding technique under nitrogen and argon atmosphere, respectively. The microstructure, micro-hardness and relative oxidation resistance of treated samples are examined by X-ray diffraction, scanning electron microscopy, micro-hardness tester and air furnace. The results show that the microstructure and cross section micro-hardness distribution of laser cladding composite coating are more uniform under nitrogen atmosphere than those under argon atmosphere, and the in-situ combustion synthesis reaction is more fully. The composite coating is mainly composed of TiN and Ti3Al phase under nitrogen atmosphere, while it is mainly composed of TiN and α-Ti phase under argon atmosphere. The average micro-hardness of laser in-situ synthesized composite coating changes gradually and increases by 40.7% under nitrogen atmosphere; however, it changes sharply under argon atmosphere. The relative oxidation resistance values of laser cladding composite coating at 600 ℃ and 800 ℃ under nitrogen atmosphere are 6.83 and 1.94 times of those of the TC4 alloy substrate, and increase by 17.96% and 19.75% than those under argon atmosphere, respectively.