A fibrous composite bicycle frame, comprising: a plurality of frame units each said frame unit comprising a fiber composite outer layer that is connected to a fiber composite outer layer of another frame unit, each frame unit including two components and at least one shaft formed by combining the two components, each said component having a foam core that is made of a foam material and a fiber composite outer layer wrapping the foam core from outside and being made of a fiber composite material, the fiber composite outer layer having a combining surface, and the two components being such fixedly combined at the combining surfaces of the fiber composite outer layers that the two components are symmetrical about where the two components are combined, wherein the foam core is a rod member having a flat surface and a convex surface; wherein the fiber composite outer layer is a tubular member having an inner flat surface abutted with the flat surface of the foam core, an inner concave surface that faces the inner flat surface and is abutted with the convex surface of the foam core, an outer convex surface, and said combining surface; characterized in that said foam core of each said component has at least one groove, and the groove is filled by a part of the fiber composite outer layer of each said component, so that the part of the fiber composite outer layer in the groove forms at least one reinforcing rib; wherein the at least one groove includes at least one first axial groove that is axially recessed on the flat surface of the foam core, at least one second axial groove that is axially recessed on the convex surface of the foam core, and at least one annular groove that is annularly and continuously recessed on the flat surface and the convex surface of the foam core; and in that the at least one reinforcing rib includes at least one first axial reinforcing rib that is connected with and formed on the inner flat surface of the fiber composite outer layer, at least one second axial reinforcing rib that is connected with and formed on the inner concave surface of the fiber composite outer layer, and at least one annular reinforcing rib that is annularly and continuously connected to and formed on the inner flat surface and the inner concave surface of the fiber composite outer layer, wherein the at least one first axial reinforcing rib protrudes in a direction different from a direction in which that at least one second axial reinforcing rib protrudes. a plurality of frame units each said frame unit comprising a fiber composite outer layer that is connected to a fiber composite outer layer of another frame unit, each frame unit including two components and at least one shaft formed by combining the two components, each said component having a foam core that is made of a foam material and a fiber composite outer layer wrapping the foam core from outside and being made of a fiber composite material, the fiber composite outer layer having a combining surface, and the two components being such fixedly combined at the combining surfaces of the fiber composite outer layers that the two components are symmetrical about where the two components are combined, wherein the foam core is a rod member having a flat surface and a convex surface; wherein the fiber composite outer layer is a tubular member having an inner flat surface abutted with the flat surface of the foam core, an inner concave surface that faces the inner flat surface and is abutted with the convex surface of the foam core, an outer convex surface, and said combining surface; characterized in that said foam core of each said component has at least one groove, and the groove is filled by a part of the fiber composite outer layer of each said component, so that the part of the fiber composite outer layer in the groove forms at least one reinforcing rib; wherein the at least one groove includes at least one first axial groove that is axially recessed on the flat surface of the foam core, at least one second axial groove that is axially recessed on the convex surface of the foam core, and at least one annular groove that is annularly and continuously recessed on the flat surface and the convex surface of the foam core; and in that the at least one reinforcing rib includes at least one first axial reinforcing rib that is connected with and formed on the inner flat surface of the fiber composite outer layer, at least one second axial reinforcing rib that is connected with and formed on the inner concave surface of the fiber composite outer layer, and at least one annular reinforcing rib that is annularly and continuously connected to and formed on the inner flat surface and the inner concave surface of the fiber composite outer layer, wherein the at least one first axial reinforcing rib protrudes in a direction different from a direction in which that at least one second axial reinforcing rib protrudes.