A microfluidic pump is a key component to controllably actuate fluids in Lab on a chip devices. To overcome technical issues of a diaphragm-type pump, a valveless nozzle-diffuser type pump was developed by utilizing the different flow resistance to control a dominant flow direction by means of diaphragm actuation. In this work, based on the operating mechanism of the nozzle-diffuser type pump, we propose a new concept of a valveless pump which can generate asymmetric flow through a pump chamber. In the proposed valveless pump, asymmetric flow path structures play a role of a nozzle-diffuser installed to a pump chamber. To validate the concept of the proposed valveless pump, we conducted CFD simulations for different geometries of the flow path structures. Based on the CFD simulations, we found that the dominant flow direction can be selectively manipulated by the pump actuation and an optimal shape of the asymmetric flow path structure was proposed to maximize the net mass flow rate through the pump chamber.