In this work, in order to investigate the behavior of non-dilute drops, including breakup,coalescence and trajectory, in a 100-mm inner-diameter horizontal swirling flow field with low inlet mixture velocity, both an experimental study and numerical simulation were con-ducted. Inlet oil phase concentration was under 3.0% volume fraction, with an inlet flowrate ranging from 12 m3/h to 18 m3/h. Malvern RTsizer and Electrical Resistance Tomog-raphy were applied for measuring the drop size distribution and oil phase concentration,respectively. Correspondingly, numerical simulations applying a Renormalization-group k-εturbulent model, coupled with a Discrete Phase Model simulating oil phase, were conductedas well. The results showed that small drops in the flow field tended to coalescence, whilethe behavior of large drops was determined by the inlet flow rate. A higher inlet flow rate ledto a thinner oil core with constant inlet oil concentration. Moreover, the simulation results,which corresponded well with the experimental observations, presented oil drops distribu-tion laws of breakup, coalescence and trajectory in a 100-mm inner diameter swirling flowfield and established a prediction model in a similar flow field. Finally, regularity of swirlingintense distribution and drop-turbulence interaction in a swirling flow field with a low inletvelocity was established. These results provide new information helpful for the design ofvane-type separator.