From the perspective of balancing performances, achieving high strength and toughness in a polymer material has caught great attention in past decades. In this work, shell-mimicking polylactide (PLA) was fabricated through a layer-assembly extrusion which combined an assembly of layer-multiplying elements (LMEs) with an extruder. By applying nine LMEs, multilayer-assembled shish-kebab morphology could be observed which was ascribed to iterative stretching and laminating effects occurring in the layer-multiplying process. When the number of LMEs was increased from zero to nine, substantial increments of 60% and 200% in tensile strength and elongation at break were achieved and a transition from brittle to ductile damage was observed. Besides, accompanied with the evolution of crystalline morphology, the surficial roughness became smaller when experiencing a scratch process. The critical normal load, a significant parameter for evaluating the scratch-resisting ability, was distinctly enlarged from 35.4 to 65.2N indicating that the scratch resistance of PLA got enhanced. High orientation of molecules was considered to be capable of resisting the mechanical deformation, while the interfacial shearing occurring between layers contributed to restraining crack propagation. Thus, it is believed that the shell-like multilayer structure developed in the layer-assembly extrusion shows a great potential in fabrication of superior PLA products with high mechanical strength and toughness.