Abstract: Through the secondary development of Fluent, the flow of polymer viscoelastic fluid was simulated by loading a user-defined function into the viscoelastic fluid momentum equation and deformation tensor transport equation in Fluent. A VOF interfacetracking method was used to analyze the deformation, breakup and coalescence process of a single droplet in the polymer melt under the cross-sectional flow field of a mixer. The dispersion process and microstructural formation mechanism of the single droplet in the complex flow field were discussed. The relevant results are instructive to explore the evolution process and mechanism of morphology development in the process of blending modification. The results indicated that the PP droplet underwent deformation, breakup and coalescence during the mixing process. The inhomogeneous deformation behavior of PP droplet happened in the C-shape zone, which resulted in the occurrence of stretching, squeezing and crossover behaviors under the chaotic flow field of interaction window. The fragmentation behavior of PP droplet included capillary instability, pinch pinching and breakup during relaxation.