Recently, the lattice gas cellular automata method has been developed to simulate the hydrodynamical phenomena by discrete lattice gas models obeying cellular automata rules. This method gives rise to macroscopic dynamics by using the simple idealized microscopic dynamics. Despite this method has made with significant contributions for complicated fluid physics, such as the now through porous media, phase separation and interface dynamics, the application was made for several typical problems in fluid dynamics and has rarely been conducted for the equipment used in the process industries. In this work, we tried to apply the lattice gas automata method to analyze the flow field in the mixing section of a single screw extruder, which is one of the most important equipment in polymer processing. The simulated result was found to correspond to that solved by the finite difference method, giving a more accurate velocity distribution.