Abstract: A direct current atmospheric plasma spray was conducted at different power levels and flow rates of argon plasma gas. In this paper,electron number density of the plasma jet was determined using Δλ_1/2 of the Ar I (430 nm) line,and the effect of different power levels and flow rates of Ar plasma gas on the electron number density in the thermal spray plasma jet was investigated. Meanwhile,the degree of ionization of Ar atom was analyzed using Saha equation,and the relations between the degree of ionization,the gas flow and arc electric current were discussed. The results show that the electron number density increased with increasing the plasma input power and Argon content of the plasma gas,while the degree of ionization increased with the increase of the plasma power but decrease of the Argon flow rate.