A self-contained hybrid actuator is a kind of a piston-cylinder device which is operated by a micro pump. The actuator is used for an air plane, a guided weapon, a vehicle, etc. since it has high actuating power and velocity although its size is small. The actuating velocity of the self-contained hybrid actuator is influenced by the actuating frequency of the pump. reed valve, and applied voltage. in this study, the influence of the actuating frequency and the reed valve on the actuating velocity was investigated by analyzing internal flow distribution. the FSI (Fluid Structure Interacting) of the ANSYS with the turbulent model of SST was used for the numerical analysis to calculate the internal flow by the pump frequency. Also, the effect of the shape and the thickness of the reed valve was studied. The output velocity form the numerical analysis increased with the actuating frequency initially, and the velocity decreased after 250Hz by the flow loss because the working fluid velocity could not follow the accelerating of the piezo pump. Also, the U-type reed valve showed higher output velocity than the original shape did because of creation of relatively small vortex.