Abstract: In this paper, a high speed fluid motion analysis system was used to investigate the liquid film morphology of the dual-orifice swirl nozzle deeply, especially on the formation and breakup mechanism of the liquid film. It was found that the liquid film formation of pilot line was divided into three stages, including jetting, forming and unfolding, while the liquid film formation of main line was divided into three stages, including clustering, forming and unfolding. The spray medium flow of the pilot line increased the atomization characteristic of the main line when the main line was open. The liquid film breakup process of main and pilot line liquid is divided into two stages, including primary breakup and secondary breakup. The liquid film primary breakup of the main line can be divided into two types according to holes on the liquid film. The liquid film of pilot line was disclosed to swing periodically. The swinging process reduced the breakup length of the liquid film and improved the atomization characteristic. With the increase of the pressure, the ratio of swinging duration of liquid film to vibration period increased. The results benefit to provide guidance for the disclosure of the flow mechanism and the basic design of the dual-orifice swirl nozzle.