The quality of combustion assisted thermal spray coating depends greatly on the flow behavior of reacting gases and particle dynamics. The present study investigates the effect of gas phase dynamics through the nozzle of a thermal spray gun by employing a numerical model. The model is developed by considering the conservation of mass, momentum and energy of reacting gases. The particle dynamics is decoupled from the gas phase dynamics since the particle loading in the spray process is very low. The turbulence effects are modeled by using a standard k-ε model. The chemical reaction is modeled by using a simplified kinetic mechanism with a finite reaction rate. The model is employed to investigate the influence of various design parameters on the coating quality of thermal spray process. These parameters include total gas flow rate, oxidizer flow rate, fuel flow rate, air fuel ratio, cooling rate, preheating of reactants, reaction kinetics, and nozzle barrel geometry.