A distribution graph of electronic pot ential and track near microtip in FFEA was obtained by finite difference simulat ing three dimensions texture of double gate FFEA.It is clearly a result that ele ctrons focusing effect becomes stronger as the focus electrode bias decreases to w ard the tip potential.If negative electrode bias,we may affirm that almost all e lectrons are repelled by the electronic lens and finally return to the grid elec trode.The potential of grid electrode almost dose not affect on the track of ele c trons from microtip by the quantum tunneling effect,which can only increase elec tronic amount as voltage based grid become more higher.The electrons being of bi gger shooting angle will be embarrassed as diameter of focus electrode reduce.