The first principles based on the density functional theory and the nonequilibrium Green's function method are adopted to research the electronic transmission of a zigzag single wall carbon tube with an implanted Li atom. The transmission model is built after optimizing the structure of the single wall carbon nano tube with the implanted Li atom. The electronic transmission and the density of states are obtained. The electronic transmission characteristics are analyzed when the electronic energy and the bias voltage vary. It is found that the conductivity changes obviously as SWCNT is implanted with the Li atom, the electronic transmission band is broadened and the quantum step effect is recovered.