Abstract: The auto-ignition with low-pressure argon stream used to ignite the arc heated wind tunnel is investigated,in order to overcome the disadvantage of the conventional ignition method, which has a long preparing time,poor reliability and safety in operation.The effects of electrode gap,gas supply way and ignition sequence on ignition performance were examined experimental-ly.Arc heater with the length of several meters was ignited first by breakdown of argon between short electrode gaps at trigger voltage and then arc elongate to anode with the close of switches in sequence .It was indicted that arc heated wind tunnel could be easily ignited with low-pressure ar-gon stream by the way of step trigger.When the electrode gap is 25mm,the ignition performance is the best,whose start time is the shortest and start arc current is the lowest.Ignition gas argon should be injected in the rare of arc heater,which could reliably ignite arc heated wind tunnel and have several advantages in operation and maintenance.And a good ignition sequence used in arc heated wind tunnel was also suggested.