Disclosed is a polyolefin resin, a method for preparing the same, and a vehicle rear bumper beam using the same. The polyolefin resin is characterized by being composed of a thermoplastic resin composite including a polymer base including a polypropylene homopolymer, which has a molecular weight distribution of 2 to 10, and a colorant; and a fiber reinforcing material that is impregnated into the polymer base and has a length of 5 to 20 mm, wherein 10 to 50 wt % of the fiber reinforcing material is included with respect to the polyolefin resin. The method is characterized in that a thermoplastic resin composite is formed by impregnating a molten mixture including a polypropylene homopolymer, which has a molecular weight distribution of 2 to 10, and a colorant with a fiber reinforcing material having a length of 5 to 20 mm.