In the last few years, a new method for surface preparation has evolved, namely thermo-abrasive blasting. This technique utilises a high enthalpy thermal jet to propel abrasive particles. The thermo-abrasive blasting gun, also called a thermal gun, is based on the principles of High Velocity Air Fuel (HVAF) processes. Some empirical data is available on thermo-abrasive blasting method and systems. To effectively improve on nozzle design and productivity, modelling of the thermo-abrasive blasting process was required. This paper describes the computational modelling of the thermal gun with computational fluid dynamic software, namely STAR-CD. The developed computational model can be applied to HVAF systems used for thermo-abrasive blasting and thermal spraying.