The structure and operating principle of micro valveless pump were investigated theoretically and experiinentally. The nlatheinatical model of pressure and flow rate within the inicro nozzle/diffuser was estsb lished to aralyze the effects of nozzle/diffuser parametels on the output flow rate of the inicro valveless pump. The experiments were carried out with different structural parameters, driving fi'equencies, vibration ampli tudes and stiffiness of the driving diaphragms. Effects of the structural parametels and driving conditiorks on the operation performance of the pump are discussed in detail. The work provides useful reference for structure op tiinization selection of the driving diaphragm of micro valveless pump.