The calibration of OES is carried out through a sodium lamp prior to conducting the experiment. The photoelectrons emitted from sodium vapor at a wavelength of 588.995 and 589.592 nm correspond to the energy level decay transformation from the upper level 3p3/2, 3p1/2 to the lower level 3s1/2, respectively. The detected signal of the plasma jet is shown in Fig. 3(a), which is obtained at a distance of 200 mm from the nozzle outlet. It is shown that the spectroscopy of hydrogen and argon emitted from electron transition intensively distributes in a wavelength range from 650 to 850 nm. The signal of YSZ within the plasma jet is presented in Fig. 3(b), which is obtained at the same distance. The data of YSZ within plasma jet are the results of electronic transformation of zirconium CI-994 and yttrium atom in a wavelength range from 500 to 600 nm. The relative major signals of Y and Zr, composing YSZ, are emitted at the wavelength of 508.82 and 566.63 nm, which correspond to the excited electrons decaying transformation from the upper level 5d5/2 to the lower level 5p3/2 and from the upper level 5p2 to the lower level 5s2, respectively. It is demonstrated that the relative intensity of signals of Zr and Y in the plasma jet is relatively low which suggests that the electron transition process in this case is low. The electron temperature of the plasma jet is also calculated about 4469 K according to the peaks of Hα and Hβ at the wavelength of 656.28 nm and 486.13 nm, respectively. The low electron temperature is consistent with the low intensity of Zr and Y in the plasma jet. However, it has been found that the phase vapor of Y and Zr exists in this plasma jet in spite of low intensity. The relationship between coating structure and OES results was also reported by Von Niessen et al. . A splat-like coating was produced when the relative intensity of the spectrum was low, and the columnar structure was obtained from the vapor phase when the relative intensity increased. As a result, OES could be used as a useful tool to characterize the YSZ evolution and then to infer the existence of the vapor phase in the plasma jet.