Devices ITO/TPD(NPB)/Cu were made.Through transforming Fowler-Nordheim(F-N) formula,the work function of ITO was measured by avoiding the influences of carrier masses and device thickness.We got the results 4.78 eV and 4.88 eV which were close to what references reported.This method simply brought to better results and provided a reference for measuring work-function of semiconductor and metal especially alloy electrodes.