Electron transport properties of (4,4) single wall carbon nanotube as well as the nanotube with oxygen molecule absorption, are investigated by using first principles analysis. The results show that electron current through the nanotube with oxygen molecule absorption system increases linearly under low bias ranging from 0 to 1.1 V, while the bias is larger than 1.1 V, the current through this system increases slowly. It is also shown that absorbed oxygen molecule brings two kinds of influence on the properties of electron transport: first, the oxygen molecular absorbed states afford new channels to electron transport and enhance the transmission. Second, the oxygen molecular absorbed states spoil the nanotube’s symmetry and enhance the electron scattering, so reduce the transmission.