In this paper effect of swirl number on mixing structure and ignition probability in turbulent non-premixed natural gas/air flame have been investigated. The flames are visualized by a digital camera and inverted by Abel transformation. Maps of ignition probability are measured by changing the spark position axially and radially while the flow field and mixing topology are established using numerical simulation. In order to study the kernel propagation high speed camera was used. Three zones were defined based on probability of successful ignition. First one called ineffective zone where probability of successful ignition was less than 20%. Second one called transition zone where probability of successful ignition was between 20% and 80% in which successful ignition is highly dependent to the spark location. And third one called high probability zone where probability of successful ignition was more than 80%. It was found that although the increment of swirl number improves the rate of mixing, it does not result in a better distribution of successful ignition probability. In fact, in high swirl numbers the high probability region is very small but at some lower levels the high probability region is distributed at the burner exit resulting better ignition characteristics.