The invention discloses a liquid fuel inner hole supersonic flame spray gun, which comprises a gun shell, a gun barrel, an oxygen delivery pipeline, a fuel delivery pipeline, an ignition line pipeline, a fuel injection nozzle, a stabilizer, a combustion chamber, a high temperature and high pressure gas convergence section, Elbow connector, powder feeding needle, gas compression throat, flame diffusion section, nozzle, water outlet at the bottom of the combustion chamber, spark plug and cooling water inlet pipe; The position where the stabilizer is connected, the spark plug is set at the position where the ignition line pipe is connected to the stabilizer, one end of the combustion chamber is provided with a stabilizer, and the other end is provided with an elbow connector, and the combustion chamber and the elbow connector are connected. The pipeline consists of a high-temperature and high-pressure gas converging section, a gas compression throat, and a flame diffusion section in sequence. The nozzle is set at the end of the flame diffusion section; the powder feeding port is located in the middle of the elbow connector. The invention can effectively increase flame speed, improve coating bonding strength and reduce porosity.