This paper reports on the design and simulation of a valveless micro pump which promises widely applicable in microfluidic applications. The structure of the pump comprises a PZT diaphragm and a fluidic network channel which can be easily fabricated by either conventional machining or silicon micromachining techniques. The working principle of the pump relies on the structure of the cross junction which connects the pump chamber, the outlet and two opposite inlet channels. This design allows a difference of fluidic resistance and momentum between the pump phases which results in a net flow from the inlet to outlet. The pump performance is studied by numerical simulation by applying the deformation of the PZT diaphragm. Experiments of the prototype had been conducted and working principle was confirmed.