A semi-empirical model of spatial SMD distribution at the near-field of swirl cup was proposed based on the physical process of swirl cup atomization and the characteristics of spatial Sauter mean diameter (SMD) distribution. The swirl cup spray at the near-field was divided into central zone and border zone

the hybrid atomization model of pressure swirl with primary air blast atomizer was used for the central zone

and the prefilming airblast atomization model of Ventruri tube was used for the border zone spray. The SMD and SMD spatial distributions of the spray were combined with Gaussian distribution simultaneously. According to the difference of air pressure drop

two types of semi-empirical models: pressure swirl atomization dominated model and airblast atomization dominated model

were validated respectively. Furthermore

the influences of liquid pressure and air pressure drop on the spatial SMD distribution were predicted and analyzed. Pediction results show that: the SMD decrease with the increase of liquid pressure or air pressure drop.