This paper presents a photoplastic investigation on the extrusion of a flat extrusion container, which uses a streamlined die to produce the integral wall-plate. Polycarbonate with good strain-optical property is adopted as the extruded material. First, the isochromatic and isoclinic fringe patterns of the extruded polycarbonate model are taken, secondly, the plastic strains of the symmetric plane of the model are acquired by a hybrid method consisting of orthographic and oblique passing, then, the stresses of the symmetric plane are analyzed by the total theory of plasticity, at last, the extrusion pressure and the friction are obtained by the stresses of the points contacted to the container and the die. The distributions of the strains, the stresses, the extrusion pressure, and the friction obtained by the experiment provide references for numerical simulations and optimized design of the flat extrusion container.