Abstract: A low-cost and high-stability microwave plasma torch source based on BJ22 rectangular waveguide was developed, which is supplied by the (2.45±0.05) GHz frequency microwave source. The entire system consists of a 1~10 kW magnetron power supply, a circulator, a tuning section and a waveguide resonator. Atmospheric open microwave plasma was produced by the interaction of the work gas and the high electrical field, which was generated between the gas nozzle and the waveguide aperture by specific tuning structure. Several key factors were simulated to get the effect of key factors on electric field strength and then the microwave resonator was designed. A variety of gases were used to produce the plasma including argon, helium, nitrogen and air. In this paper, the basic characteristics of the