Abstract: Discharge and flow characteristics of a three-electrode plasma synthetic jet actuator have been experimentally studied by discharge measurements and high-speed shadowgraphy technology. The influence of capacitor, cavity volume and exit diameter on flowfield and speed of the actuator were analyzed. Results show that the discharge is a typical underdamped discharge and the period includes discharge trigger, discharge enhance, discharge decay and arc off. The flowfield of the plasma synthetic jet is composed by main jet, precursor shock and complicated reflect shock. Jet speed will increase with the increase of the capacitor and exit diameter and decrease with the increase of cavity volume. All of capacitor, cavity volume and exit diameter have threshold value, when the capacitor and exit diameter are less than the threshold value, or cavity volume greater than the threshold value, the speed of the precursor shock is invariant and is about 345m/s. Otherwise, the variation trends of the precursor shock speed are similar with the jet.