A 1.6 cm long argon plasma jet torch is generated by using hollow needle to plate discharge device working in atmosphere. Rotational temperature, vibration temperature and electron excitation temperature are studied by using optical emission spectrum. Optical emission spectrum is collected from 300~800 nm, which consists of strong Ar I lines, N2 second positive band system, weak OH－ around 309 nm and N+2 lines. Rotational temperature is obtained by simulating the spectrum shape of OH－radical band with program of “LIFBASE”. Gas temperature is 500 K and keeps a constant number at different positions along the plasma. Vibration temperature is calculated using N2 second positive band system, electron excitation temperature is obtained using spectral line intensity ratio. Spatial distributions of the above two kinds of temperatures are similar; they decrease firstly and then increase with the increase of the distance from the arc root.