Extrusion is an efficient and versatile process for pulse-based food processing that leads to starch melting and protein aggregation. The texture of these extruded foods depends not only on their density and cellular structure, but primarily on the mechanical properties of the cell wall material, considered as a dense starch/protein composite material. This work aims to study the morphology and to determine the constitutive laws of this material. Dense pea-based composites of various composition (pea flour and blends Starch/Protein: 2/1, 1/1, 1/2) are processed by twin-screw extrusion under various thermomechanical conditions (SME=102-103kJ/kg). Their viscous behavior, determined on a capillary rheometer with pre-shearing, depends first on S/P ratio, and can be used to simulate the extrusion, thanks to Ludovic® software. Various composite morphologies, dispersed and co-continuous, are evidenced by CSLM, and their images are quantified by (%) protein area and interface index. The mechanical properties of composite depended not only on particle (protein+fibers) volume fraction and morphological features, but also on local mechanical properties of the phases and interphase, which were determined by nano-indentation. The experimental results are integrated in a finite element mechanical model based on composites microstructure. The model revealed a significant stress localization at starch-protein interphase.