Suspension polymerization of methyl methacrylate (MMA) has been considered as a liquid-liquid reactive polydispersity system, which involves the complex multiphase flow behavior at multiple time and length scales. The polymerization kinetic characteristics (i.e., gel effect and glass effect) and liquid-liquid dispersion phenomena (i.e., breakage and coalescence of liquid droplets) appearing in this process make the study of suspension polymerization complicate. In this work, a three dimensional (3D) multiscale model including Eulerian-Eulerian two-fluid model, polymerization kinetics model, population balance model (PBM) and some other constitutive models was developed to elaborate those multiscale phenomena in polymerization course. The current model was validated using the reported data in terms of conversion, molecular weight as well as droplet Sauter diameter. The developed model was then employed to investigate the influence of key operating conditions on polymerization kinetic characteristics and liquid-liquid dispersion phenomena. Furthermore, the effects of reactor structure on droplet breakage and coalescence were studied in detail. This simulation work may contribute to the preparation of polymer products and the scaling up of stirred tank polymerization reactors with multiphase flow and multiscale characteristics. (C) 2017 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.