In this study, a cut diameter prediction equation based on the design parameters of an axial flow cyclone was derived by modifying the conventional correlation for a tangential flow cyclone. Among the parameters of the cut diameter prediction equation for a tangential flow cyclone, the effective number of turns and the inlet width, which are difficult to define for the geometry of an axial flow cyclone, were formulated in terms of the design parameters of the axial flow cyclone. Experiments were conducted by varying five design parameters, the vane angle of the swirl generator, the body length of the cyclone, the flow rate of the working fluid, the effective swirl length, and the diameter of the vortex finder, and statistical analysis was performed to compare the cut diameters obtained from the experiments with those calculated using the developed model. The coefficient of determination (R²) and the mean absolute percentage error (MAPE) of the cut diameter calculated using the developed model were 0.83 and 4.82%, respectively, indicating high prediction accuracy and reliability. In addition, the model exhibited a low bias of +0.25%, suggesting minimal systematic error, and a concordance correlation coefficient (CCC) of 0.911, confirming the excellent agreement between the model and the experimental results.