Volume of fluid (VOF) method combined with primary breakup model (PBM) is developed to model large flow rate pressure-swirl nozzle used in pressuriser of the pressurised water reactor (PWR) power plant system. For the VOF model, the renormalisation-group (RNG) K–ϵ model is selected to ensure the accuracy of simulation for swirling flows. The 3-D transient flow is simulated and the dynamic stability of the injection pattern is analysed for the nozzle. Based on the growth rate of the disturbance at the interface of the two phases, PBM is embedded in the VOF model in the form of user defined functions (UDF) to investigate the further breakup from sheet to spray drop and predict the spray drop size spectrum. In addition, experimental studies, considering the characteristics of mass flow rate, spray cone angle, spray flux distribution and drop size spectrum, were conducted to verify accuracy of the numerical results. The result of comparison shows that there is good agreement between the simulated results and the experimental data. Especially, the distribution tendency of the spray drop size simulated by PBM fits the experimental value well and the drop size corresponding to the maximum probability is predicted successfully. The present investigation shows that the VOF–PBM methodology can be applied to simulate the pressure-swirl nozzle and optimise design of spraying systems.