Numerical simulation of flow field of high velocity oxygen fuel thermal spray process of Diamond Jet is presented by studying the influence of divergent angle on combustion flow field with CFD. It is shown from the results that the site of appearance of Mach cone is controlled by the divergent angle, and the site will deviate towards the combustor with the angle increasing. When the angle is within 0°-3.0°， the magnitude of Mach number increases with the angle increasing. The divergent angle affects the temperature within the Diamond Jet. When the angle is within 0°-1.0°, the temperature decreases with the angle increasing, which means energy transfer from combustion energy to kinematic energy. But with the continual increase of the divergent angle, the temperature decreases no longer. These maybe present some clue for the design of Diamond Jet spary.