Abstract: The basic characteristics of a gas tunnel type plasma jet which is ejected into the open air are experimentally investigated.To clarify the properties of the gas tunnel along the center axis,the pressure in the vortex chamber of the torch was measured in the absence of the plasma jet.The pressure in the gas tunnel is as low as 230×1.33×10² Pa along the center axis with a gas diverter nozzle 4~8 mm in diameter.The plasma jet produced in this low-pressure gas tunnel is longer than a conventionally produced jet and has superior characters as follows.It has an extremely positive volt-ampere characteristic,and very high potential gradient,such as 41 V/cm at 400A when a gas diverter nozzle 4 mm in diameter is used,and high thermal efficiency and high energy density.In this apparatus the supplying method of the spraying powder is different from the conventional type.For this reason,the quality of the spraying coating can be pimproved remarkably.