As for metal matrix composites (MMCs), the selection and application of reinforcements play a vital role in their comprehensive properties. In this work, the CrCoNi medium entropy alloy (MEA) was selected as reinforcement for Al matrix composites, and the effects of the content of the CrCoNi MEA on the mechanical properties and friction resistance were systematically investigated. It was found that the CrCoNi MEA can effectively improve the mechanical properties of the Al matrix composites, especially the 5 wt.% CrCoNi/Al composite can achieve a high strength without the sacrifice of ductility, due to the strengthened interfacial bonding between the Al matrix and the CrCoNi reinforcements caused by the element interdiffusion and the high mechanical performance of the CrCoNi MEA itself. In addition, the wear resistance of the composites can be enhanced by the inclusion of the CrCoNi MEA reinforcement, because the CrCoNi MEA can substantially improve the hardness of the composites and promote the formation of the oxidative protection film during the friction process. This work paves a new route for preparing Al matrix composites with high mechanical properties and friction resistance.