Abstract: Plasma actuators have been become the research focus in flow control and fluid dynamic fields because of the advantages of simplicity, fast response and robustness. Compared with typical two-electrode actuator, three-electrode Plasma Synthetic Jet Actuator(TE-PSJA) possesses the advantages of higher energy efficiency and bigger jet impulse, and has potential to be adopted as a fast-response direct force generation device. In order to reveal the effects of geometric parameters on the flow field and impulse, discharge characteristic, flow field and impulse of TE-PSJA with different orifices, volumes and electrode gaps were experimentally studied using electric parameter measurement device, high-speed shadowgraphy and single line torsion pendulum system. In order to compared the working characteristics of the actuator in different conditions, dimensionless energy deposition ε and dimensionless jet impulse I^* were defined, and the effects of geometric parameters on ε and I^* were analyzed. Results showed that the best jet orifice diameter is existed, ε and I^* decreases as volumes increase, but increases as electrode gaps increase, strength and affected area of the jet decrease as volumes increase, while increase as electrode gaps increase. A similar flow structure which contains a mushroom-shaped jet and a spherically symmetric precursor shock above the jet front was observed. Compared with the variation of I^* with ε on the different volumes and electrode gaps conditions, it can be concluded that in order to design actuators which possessed better jet impulse level, the dimensionless jet impulse I^* should be increased as possible with the same ε. The cavity volume should be increased so as the dimensionless energy deposition ε is to be the design value when the dimensionless energy deposition is less than the initial case. On the contrary, the electrode gaps should be increased so as the dimensionless energy deposition ε be the design value when the dimensionless energy deposition is larger than the initial case.