The outstanding combination of selectivity and permeability observed in ultra-thin nanoporous mem-branes attracts broad interest from both fundamental research and practical application aspects.It is reported that the asymmetrical ion transport can be realized through the modification of polyelectrolytes on the outer membranes surface.However,the related mechanisms are still unclear which hinders their applications.Herein,we systematically investigate the origin of the ion current rectification in heterogeneously charged ultra-thin nanopores.The calculated results based on the continuity model suggest that,the ion transport across the ultra-thin membrane is dominated by the charge on the outer membrane surface rather than the pore wall.The overlap of electric double layer outside the pore entrance is essential for the ion asymmetric transport.And it accordingly results in the fact that the ion concentration enrichment and depletion effect occurring outside the nanopore orifices governs the high and low ionic conductance states under the applied bias.These features can be regulated by the membrane surface state,which is truly attractive be-cause the surfaces of the outer membrane can be easily modified by experimental approaches.These findings provide the renew inspiration for the de-sign of high-performance 2D nanofluidic devices.