For the purpose of designing a high performance synthetic jet actuator, the performance of actuators has been investigated experimentally for a range of geometric parameters. It is showed that the performance of a synthetic jet actuator is determined by these geometric parameters, the square/rectangle exit-slot is propitious to found a powerful synthetic jet, and the maximal velocity of actuator with dual-membranes is doubled compared with the actuator with a single-membrane. It is also found that varying the pressing states of membrane does not change the main relations between synthetic jets and the exciting frequency but affects the synthetic jet velocity values a lot.