Abstract: Pressure swirl atomizers are widely used in aircraft engine combustion chamber to their simple and reliable structure as well as excellent atomization performance. The atomization characteristic of pressure swirl atomizers influences the combustion stability, combustion efficiency, and emission characteristics. This study systematically analyzed the liquid film, breakup mechanism, and atomization characteristics of pressure swirl atomizers. The goal was to establish a correlation between the morphology of the liquid film and atomization characteristics, thereby supporting the optimization of pressure swirl atomizers' performance. Phase-Doppler Particle Analyzer (PDPA) and high-speed shadowgraph were employed to investigate the impact of fuel injection pressure on parameters such as discharge coefficient, spray angle, liquid film breakup mechanism, and droplet size distribution. Additionally, the Proper Orthogonal Decomposition (POD) method was utilized to identify primary and secondary breakup modes for different liquid films. The result shows that with injection pressure increased, the discharge coefficient and spray cone angle exhibited a trend of initially increasing and then decreasing. The fuel injection pressure alerts the liquid film by changing the liquid Weber number ( We ). With the We increased, the breakup length of the liquid film gradually decreased, and the droplet radial velocity increased. This caused the larger droplets to move towards the sides, resulting in a rapid decreased in the Sauter mean diameter (SMD) at the center of the spray cone. The liquid film breakup processes were composed of a variety of modes. With the We increased, the primary modes are varied from the impact breakup to wavy breakup and perforation breakup as well as turbulent breakup and the surface wave frequencies of these four breakup modes increased in succession.