Abstarct: In this study, the propagation of a high intensity laser pulse in the background gas of one atmosphere (oxygen, nitrogen and air) is investigated. For this purpose, using Maxwell equations, the equation governing the laser pulse propagation is obtained. This equation generally includes the nonlinear effects of self-focusing, Raman scattering, plasma defocusing, plasma Wakefield, relativistic effects, and the pulse energy depletion due to the ionization. However, regarding the laser pulse self-guiding, the terms of plasma defocusing, self-focusing, and the pulse energy depletion due to the ionization are more important than the others. To investigate the laser pulse self-guiding, the equation of the laser spot size is obtained using the SDE method. Then its variations with time over the pulse duration and also with position in the propagation path for the oxygen, nitrogen and air are investigated. Our results show that there is a greater degree of divergence behind the laser pulse due to the presence of plasma. Moreover, the pulse divergence increases with the propagation length. Study of the laser pulse intensity shows that the intensity is inversely proportional to the degree of divergence. Therefore, the greatest decrement in the laser pulse intensity is observed behind the pulse and then in front of it. The least intensity decrement occurs in the middle of the pulse. Investigation of the electron density also shows that the changes in the laser intensity and the electron density are directly related.