In this report, the distribution and deviation of electric field in the active medium of the TE CO2 laser has been investigated due to the injection of net electron charge beam as a plasma generator. Some parameters of system have been considered, such as density and mean-free-path of injected charge beam. The electric potential and electric field distribution have been simulated by solving the Poison’s equation using the method of successive over relaxation (SOR) numerical method. The electrode potential and the number of injected charged particles are respectively considered to be +75 kV and 108 mm-3. In these conditions, the maximum energy of the electrons beam would be at the order of 1-2 eV. Deviation of the electric field with different mean-free-path of electrons beam with Gaussian density distribution has been numerically calculated. It has been concluded that if the net charge density is increased then the field deviation would grow. Moreover, if the mean-free-path of the electrons is decreased, subsequently, the electric field deviation is increased.