The 3 K and 6 K (meaning that 3000 or 6000 carbon filaments are contained in one bundle) carbon fibers were embedded by pure aluminum sheets to have a sandwich composite structure under the accumulative roll bonding method. The tensile and cupping tests were carried out to reveal the strengthening mechanism of carbon fibers embedded in the aluminum+carbon fibers composite sheets. The improvements of ultimate tensile and cupping strengths of aluminum+carbon fibers composite sheets reached to be as high as 48 % and 38 %, compared with that of as‐received sheets. With the detailed observation of the tensile and cupping fractures, the underlying strengthening mechanism comes from the bridging effect of carbon fibers during tensile and cupping tests. The accumulative roll bonding method was approved to be an effective way for aluminum+carbon fibers composite sheets preparation with higher tensile and cupping strength.