Abstract: The detailed near-wake flow behind the EBMC flameholder and V-gutter flameholder was measured by using 2D cross-correlation on-line PIV in a low speed wind tunnel.On the basis of the research on the instantaneous flow,the instantaneous viewpoint about the flame stability mechanism is put forward.Alternative formation and shedding of vortices in the near-wake flow structure have important effect on the flame stability.Large scale vortex provides essential condition for flame spreading as ignition source.And it transfers the energy and radicals to the forming vortex which becomes the ignition source as its development.So the source is handed on with the alternative formation and shedding of vortices.The larger is the scale of vortices and the more stable are the vortices, the better is the flame stability.