Graphene-reinforced 7075 aluminum alloy composites with different contents of graphene were prepared by spark plasma sintering (SPS). The structure and mechanical properties of the composites were investigated. Testing results showed that the hardness, compressive strength, and yield strength of the composites were improved with the addition of 1.0% graphene. A clean, strong interface was formed between graphene and the metal matrix via metallurgical bonding on the atomic scale. Harmful aluminum carbide (Al4C3) was not formed during SPS processing. Further addition of graphene (3.0%–5.0%) deteriorated the mechanical properties of the composites. The agglomeration of graphene plates was exacerbated with increasing graphene content, which was the main reason for this deterioration.