In spray painting and coating industries, air-blast injectors configured with a liquid-centered and two-stage gas nozzle have many advantages, including low paint bounce-back and high transfer efficiency. Experimental investigations are used to study overspray characteristics and transfer efficiency. To verify the effect of the gas jets, air-blast injectors with a gas post of two stages are designed to analyze the overall spray characteristics as well as to increase the transfer efficiency. The experimental results show that the liquid jet breakup is governed by the gas jets of the inner stage In the case of the inner stage gas injection mode, better atomization qualities can be achieved. However, in the case of the outer stage gas injection mode, larger droplet distributions appeared at the same measurement point. As the momentum ratio of the gas jets increased, the droplet sizes decreased. Additionally, the gas jets of the outer stage also contributed to the atomization at the far-field spray region, and it also contributed to the droplet transportation to the object. It was observed that, as the velocity of the gas jets increased, the mean drop diameters decreased and the transfer efficiency increased due to the outer gas post which caused an air curtain to surround the spray jets so that an impinged droplet could not overspray to the outer region of the spray jets.