Considering the serious oxidation of titanium alloy induced by laser cladding in air, a coaxial nozzle with shielding gas is designed to protect the molten pool. A three-dimensional numerical model of the coaxial cladding nozzle with inside-laser powder feeding is established using FLUENT software, and the influences of the inlet number, angle, and flow rate of shielding gas on the mass fraction of argon are analyzed. The results demonstrate that the inlet number of the shielding gas is related to the symmetry of argon distribution. The inlet angle has little effect on the mass distribution of argon; however, increasing the flow rate of the shielding gas will greatly improve the effective protection domain. According to the optimized parameters of the coaxial shielding gas nozzle, the laser cladding of the Ti-6Al-4V alloy in an open environment is conducted by using argon as the shielding gas. The surface of the molten track presents silvery white and the cladding layer is fine, indicating that the coaxial gas nozzle can effectively protect the molten pool from oxidation.