Two atmospheric pressure microwave plasma jet (MW-APPJ) devices with different nozzle structures are designed which are based on the coaxial transmission line structure. The frequency is 2.45 GHz and working gas is argon. What's more, the effects of two different nozzle structures on the characteristics of plasma discharge have been studied. Based on the electromagnetic field simulation results, the MW-APPJ generates a high-intensity electric field at the nozzle. After optimizing the structure, the field strength at the nozzle have reached the breakdown field strength required for argon ionization under the frequency of 2.45 GHz. Meanwhile, the simulation of the argon flow distribution was carried out under steady-state using multi-physics coupling simulation software. In addition, the basic characteristics of the atmospheric pressure argon plasma jet under the two nozzle structures were compared and analyzed through experiments. The experimental results show that different nozzle structures can affect the variation of reflection parameter with input power, but do not affect the variation of plasma jet length with input power and the variation of reflected power with inlet flow; at the same time, under atmospheric pressure, the steady-state microwave plasma jet exhibits metal-like property and the electrons in the plasma can only absorb microwave energy in a very thin area, which causes large reflected power of the microwave.