The phenomenon of small angle light scattering (SALS) has been applied to the actual extrusion molding process. The current study utilizes a self-designed mold with built-in windows for observation of polymer melts within a slit die. A high-speed charge-coupled-device (CCD) camera is used to record the SALS images in real-time with different process conditions for subsequent analysis. Modification algorithm has been proposed to eliminate the effect of multiple scattering. Flow behavior of polymer melts is simulated and analyzed by real-time SALS image processing technique. Visualization is performed via a high-performance computer-aided analysis software which allows on-line data acquisition and characterization the flow field of polymer melts.