Abstract: In order to further investigate the influence of focusing gas flow on the working stability of high capacity plasma torch,two kinds of water cooled sensors were designed and applied to the YJ-700 high capacity plasma torch with annular water cooled focusing gas shroud and the commercial LH-300 plasma torch for determining,under different parametars and different nozzle orifices,the radial distribution of arc pressure,the heat transfer from arc to sensor and the radial temperature distribution of the internal surface of sensor.The acting force of the arc to the sensor is different from that to the molten pool,nevertheless it can be adopted to describe quantitatively the stiffness and the penetrating power of the arc.Though the temperature distribution of the internal surface of the sensor is not the same as the actual radial temperature distribution of the arc,and the heat transfer from arc to sensor is not equivalent to the heat transfer from arc to the anodic workpiece,they may explain the thermal characteristics of the arc and the rule of heat transfer from arc to anodic workpiece.It is demonstrated that not only the double arc can be inhibited by the presence of the focusing shroud and focusing gas flow,but also the sensitivity of the pressure characteristic and thermal characteristic of the arc to the change of the plasma gas flow rate can be lowered.The influence of the change of nozzle orifice on the temperature distribution of the internal surface of the sensor can also be decreased.These are all benefitial to the working stability of plasma torch.