The welding property was decided by the physical characteristic of the arc plasma, and the dynamic property of two-element arc plama which was produced by pulse tungsten inert gas welding(P-TIG) with hybrid shielding gas was analyzed, which provides a theoretical basis for further research on the physical process of weld in hybrid gas shielded welding. Argon-nitrogen arc plasma was used to improve penetration since it has high thermal property, but demixing during welding complicated its physical characteristic. Spectral diagnosis is the most important means to measure the physical characteristics of arc plasma, but the further research on the arc characteristics of P-TIG welding with hybrid sheilding gas is still needed, especially during the arc ignition time. In this paper, an argon-nitrogen arc plasma produced by P-TIG welding during arc ignition is studied, the high-speed camera experiment system is proposed to collect the dynamic spectrum information of arc plasma, and the dynamic intensity of Ar Ⅰ 794.8 nm and N Ⅰ 904.6 nm under P-TIG welding arc was obtained; temperature and concentration of 1, 2, 3 and 4 mm under tungsten during arc ignition were calculated by Fowler-Milne method; and the physical characteristics of 80%Ar+20%N2 shielded P-TIG welding arc plasma were quantitatively analyzed. The results show that the change of arc intensity, temperature and concentration is synchronized with the current. The welding current reaches a stable state within 3 ms, while the intensity, temperature and concentration of the arc plasma take longer time to reach equilibrium state. From arc ignition to steady burning, the arc intensity presented a trend of increasing first and then decreasing during the base and peak period. As a result of changes in heat conduction and current density of the cathode, the peak temperature and base temperature in the axial position of arc plasma increase rapidly and then decrease slowly. Due to the impact of particles collision and friction, the concentration of argon decreases rapidly and increases slowly during both the peak and the base period of arc plasma, and is lower than the original value.