Abstract: Experimental results proved that submicrostructure existed in short carbon fiber reinforced injection-moulded polyetherether ketone (PEEK) composites. The thickness of skin and core layers could be characterized by the metallographic optical microscope. Mechanical properties of the full plate could be calculated by the rule-of-mixture approach, in which the separately determined tensile strength and elastic modulus of the skin and core layers were combined with regard to their relative contribution to the full thickness of the original sample. The great thermo-stress and anisotropic mechanical properties between the skin and core layers resulted from different fiber orientations and PEEK crystallinities. Therefore, correlation of submicrostructure and mechanical properties of skin and core layers with the processing condition and mould configurations became one of the most important work for the product design of short fiber reinforced injection-moulded plastics composites.