The high-frequency method may possibly disrupt operation of peripheral equipments and is harm to human body in tungsten inert gas (TIG) arc welding process,so a new method that the laser induced plasma ignites the TIG arc is presented. In this paper,a pulsed CO2 laser with pulsed width of 10 ms is used to ignite the TIG arc. A high-speed visual sensing system is established to detect the process of laser induced plasma triggering arc discharge and the shape of plasma. The experimental results show that the shape and volume of laser plasma are ones of the key factors. And only when the laser plasma contacts the tungsten rod,which therefore results in producing electron emission and forming self-maintaining discharge,the TIG arc can be ignited. Furthermore,the influence of main factors,such as shielding gas,workpiece materials,defocusing distance,and flow of shielding gas etc.,on the shape,the volume and the performance for triggering arc discharge of laser plasma are studied.