High frequency excitation is increasingly substituting for dc discharge excitation of the high power CO2 laser, in general, a great quantity of helium is applied in a common high power CO2 laser. In order to reduce the operation cost of CO2 laser, a helium-free transverse flow CO2 laser excited by high frequency has been researched. In this paper, some of the investigations of discharge characteristic and output characteristic are presented. It is shown that, under our experimental condition substituting Ar for He in the CO2 laser, the maximum input discharge power density is stable up to about 21 W/cm3, the output laser power and photoelectric efficiency are 600 W and 13%.