The material properties of heterogeneous polymer blends are crucially influenced by their morphology, i.e. by the spatial structure of the blend components. In order to understand the experimentally resulting morphologies, the dynamics of the morphology formation have to be modeled. The discussed model consists of a system of partial differential equations based on a modified Cahn-Hilliard equation, the continuity equation, and a modified Navier-Stokes equation. It includes the essential material and processing parameters like surface tension, viscosity and volume fraction of both polymers, and imposed shear rate. For the simulation of a two dimensional model a numerical algorithm was developed. Simulations show a variety of morphologies in dependence on the processing parameters that qualitatively correspond to experimental results.