Cyclone multiphase flow in the annular space is widely used in fluid machinery, such as burner and pneumatic conveying. However, the annular flow field is complex, and the related research is not sufficient. To improve the safety and efficiency of equipment, this paper proposes a method for detecting the motion state of swirling fluid in annular space by integrating computational fluid dynamics (CFD) and electrical capacitance tomography (ECT), calculates the motion characteristics of swirling multiphase flow in the annular space using the CFD, and visually measures the distribution and motion state of swirling multiphase flow in the annular space using the ECT. Numerical simulation and experimental results show that the results of the two methods are in good agreement, indicating that the model selected in this paper in the CFD is correct. The CFD effectively reveals the distribution of swirling multiphase flow in the annular pipe, and the ECT can accurately reconstruct the position and size of swirling multiphase flow in the annular space. The combination of these two methods provides a new idea for the study of multiphase flow in annular space. © 2024 SPIE.