Processing, structure, property, and performance have been acknowledged in a linearly linked picture for materials manufacturing. It is promising to harness the processing-structure relationship to accelerate the development of functional materials. In the present study, we attempted to predict microstructures of a polymer composite via computational simulations, because functions of the polymer composite would respond to its microstructures. A program KAPSEL, which has been widely utilized to calculate dynamics of solid particles in coherent fluids, was slightly amended to handle parameters related to interfacial science. Constituents of the target polymer composite were α-alumina and poly(methyl methacrylate). When proper parameter values are given, the program yielded microstructural features similar to those found in an experiment. Nimbleness and affordability of the simulation scheme would allow us to omit experimental trial-and-error for functional polymer composites.