The aim of this work is focusing on the behavior of internal and external twin-fluid atomizer using different helical grooved of air and water pathways, respectively. The present atomizer comprising a liquid inlet, an gas inlet arranged to receive a pressurized flow of air. A water flow path extending from the liquid inlet to a liquid stream outlet, and a helical air flow path extending from the gas inlet to a location adjacent the liquid stream outlet, which impinges on a liquid stream passing out through the liquid stream outlet for atomizing the liquid stream. There are many parameters affecting the behavior of that spray. The spray performance of that atomizer has been studied by investigating the discharge coefficient of the liquid, the mass concentration and the spray cone angle. Therefore, an experimental test rig is built-up. The effects of air injection pressure, helical geometry, length to diameter ratio (l/d) of mixing zone and air water ratio (AWR) have been considered. The injection pressure of air varies up to 0.5 MPa, the l/d ratio of the mixing zone varies up to 3.0 and the air to water ratios varies up to 17. The results show that, as the air mass flow rate increases in all difference water pressures, the discharge coefficient decreases, but it increase by increasing the l/d. The triangle shape of helical groove has gross effect on spray characteristics. Spray cone angle increase with the air pressure increase, while it decreases with l/d increases at the same air pressure. As l/d is decreased the mass concentration has a wider radius as compared with first one.