A scanning electronic microscope (SEM) was used for observing the microstructures of a Cockle shell. It showed that the shell is a kind of natural bioceramic composite consisting of aragonite sheets and organic collagen matrix. The aragonite sheets are further composed of aragonite fibers. The aragonite fibers are of long and thin shape and compose various reinforced microstructures, which include a kind of fiber-intersected reinforced one. The fiber-intersected reinforced microstructure was employed as the design example for the structure of man-made fiber-reinforced composite, a kind of fiber-reinforced composite with the fiber-intersected reinforced structure was biomimetically fabricated. The fracture toughness of the biomimetical composite was tested and compared with that of the conventional composite with fiber-parallel structure. It indicated that the fracture toughness of the biomimetical composite is markedly larger than that of the fiber-parallel composite.