In this paper the distribution and non-uniformity of electric field resulted of the main electrodes and pre-ionization in the TEA CO₂ laser is investigated using SOR method.  Also the difference in uniformity of electric field related to Corona and Spark Array pre-ionization methods are compared. The results show that the deviation of the electric field in Spark Array Model is more than Corona model. Besides, it has been shown that using electrodes with curved active area edges the field deviation can be reducedd to acceptable level.