A 1.6-3 cm long plasma torch was generated when argon gas was introduced by using a hollowneedle-plate discharge device working in atmosphere. The vibrational temperature and the gas temperature at plasma root and tip were studied by using optical emission spectrum at different argon gas flow. The gas temperature was obtained by comparing experimental line shape of OH radicals band around 309 nm with its simulated line shape. The vibrational temperature was calculated using N2 second positive band system Ｃ ３Πｕ-Ｂ ３Πｇ. It was found that the gas temperatures at arc root and arc tip are equal and they decrease with the argon flow rate increasing. The gas temperature decreases from 350 to 300 K when argon flow rate increases from 3.0 to 6.5 mL·min-1. The vibrational temperature at arc tip (1 950 K) is higher than that at arc root (1 755 K) under a low gas flow rate (e.g. 3.0 mL·min-1). With gas flow rate increasing, the vibrational temperature at both tip and root decreases, but the decreasing rate at arc tip is faster than that at arc root. When gas flow is larger, the vibrational temperatures at tip and root tend to be equal.