This report proposed the injection molding method of thermoplastic composite materials reinforced by the glass fiber extracted from FRP waste. Glass fiber was pre-treated by card machines and mixed with PP fiber. The sliver-type glass/PP mixture was fed into the injection molding machine directly. As a result, the glass fiber reinforced PP composites were obtained. The mechanical properties of the fiber reinforced composites were measured and discussed. It is concluded that the extracted glass fiber is good for the reinforcement of composite. The result suggests that the injection molding method described herein shows promise for contributing toward the material recycling of glass fiber extracted by the normal pressure dissolution method.