Abstract: The swirl nozzle aperture used in flue gas wet desulfurization is usually large. Its atomization particle size has a specific rule of distribution in space，which is different from other atomization applications. This rule directly affects the design of this kind of swirl nozzle and the atomization system in a desulfurization tower. Malvern laser particle size analyzer was used to study atomized particle size spatial distribution of the swirl nozzle. In order to analyze，the spatial distribution, the average particle size，particle size relative deviation and average span of single flow particle size distribution were defined. The analysis result indicated that the atomization particle size and atomization particle size distribution of the large aperture swirl nozzle showed specific rules with different flow rates and outlet positions. At all flow rates, particle size relative deviation was the largest，Sauter average particle size fluctuated in a large range，span of particle size distribution and average span of particle size distribution was the smallest at 90° angle with incoming stream. This result showed that dispersion degree was small and atomization uniformity was good at 90° angle with incoming stream. The average particle size was in power function relation with pressure and the average span of single flow particle size distribution was linear with pressure.