Abstract: Gliding arc discharge (GAD) has been widely used in the fields of energy utilization, environmental protection, and material treatment. The flow rate and type of the working gases have been reported as the important factors affecting the characteristics of GAD. To optimize the operation parameters and provide the theoretical supports for practical applications, electrical signals and discharge images were collected by electrical and optical measurements when different working gases (e.g., CO₂, H₂O and O₂) were used at different volume concentrations. The discharge mode, the voltage-current characterisitics, the spectral characteristics and arc motion characteristics of an AC GAD plasma under different operating conditions were systematically studied. The results show that two discharge modes including the steady arc gliding mode and breakdown gliding mode are observed during the GAD process when using N₂ as the working gas. The former discharge mode exhibits higher average discharge power and gliding period as well as the larger arc length and arc height. The composition of the gas addition and its volume concentration show a significant influence on the discharge mode of GAD. The addition of H₂O facilitates the formation of steady arc gliding mode, while the addition of CO₂ and O₂ makes the GAD to be dominated by the breakdown mode. The emission intensity of the active species induced by the GAD is also directly affected by the discharge mode. Compared with the breakdown gliding mode, the emission intensity is much higher when the plasma discharge is under the steady arc gliding mode, which facilitates chemical reactions. In addition, the introduction of CO₂ and O₂ into N₂ GAD may generate new active substances, such as CO and O atoms; however, the intensity of excited state nitrogen particles will decrease and the plasma region will become smaller when these second gases are introduced, and the discharge tends to be unstable under these conditions. With the addition of proper amount of H₂O, which favours the arc development and maintaining with the aid of gas flow and leading to a higher arc length and height. Due to its electronegativity of water, the electron density in the electric field decrease with further increasing the amount of H₂O, which inhibits the development of arc and the length and height of arc are gradually reduced, consequently reducing the plasma area.