Based on Bloor & Ingham's approach for determining the fluid field and on the analyses of loci of fluid particles inside hydrocyclones, analytical models are developed for calculating the migration probability of single-cone and two-cone hydrocyclones separating light dispersions. The calculated results are in good agreement with Thew's correlation at different flow rate, split ratio or fluid properties if the structural parameters keep the same as those of Thew's 35 mm hydrocyclone. The difference between predictions according to two-cone model and single-cone model is nearly negligible, which is very close to Thew's original idea that major separation happens in the small cone-angle zone. Calculated results indicate that split ratio has little effects on reduced migration probability at least for F less than or equal to 20%, which is consistent to the conclusion drawn from Thew's correlation that reduced migration probability will remain constant when split ratio changes. Because no simplifying hypothesis is imposed on structural parameters, the presented models can also be reliably applied in predicting the effects of those parameters on migration probability.