•There are rotational flow, flow through one perforation and flow through two perforations in a tridimensional rotational flow sieve tray (TRST).•The main characteristic of the flow through one perforation is the conversion between rotational liquid film and perforated liquid column.•The flow through two perforations has a more prominent shear effect on the fluid.•The flow through one perforation in the liquid phase was dominant, and the rotational flow in the gas phase was dominant.•The proportions of rotational flow and flow through perforations in coupled state in the TRST are determined. Tridimensional rotational flow sieve trays (TRST) have a variety of gas–liquid flow structures, such as rotational flow, flow through one perforation and flow through two perforations, it is important to have a deep understanding of the coupling and distribution laws of rotational flow and flow through perforations for the selection and regulation of actual working conditions. In this study, the flow structures and proportions for the rotational–perforated coupling flow in a TRST were analyzed and predicted using the measured distribution ratio for the three-blade unit. The results showed that the gas phase mainly flowed in a rotational pattern, and its proportion was approximately 62%–83%. The proportion of flow through perforations in the liquid phase was relatively large, and the proportion of flow through one perforation was approximately 51%–57%. The proportion of flow through two perforations was approximately 27%–29%.