For metal matrix composites (MMCs), the sintering temperature is of vital importance in realizing a dense bulk material with tight interfacial adhesion as well as limited structural damage to reinforcements. In this work, we investigated the influence of the spark plasma sintering (SPS) sintering temperature on the microstructure and mechanical properties of the in-situ synthesized discontinuous three-dimensional graphene-like network (3D GN) reinforced copper matrix composites . It demonstrates that with the rise of the sintering temperature from 600 °C to 700 °C, the GN distribution changes from intergranular type to intragranular type as a result of the significant improvement in interfacial wettability . Furthermore, the overall mechanical performance (both tensile strength and ductility) of the GN/Cu composites presents an unanticipated declining trend at elevated sintering temperatures. Integrated with microstructure characterization and the theoretical analysis, it is verified that the change of the reinforcement size and its distribution are the dominant factors. Their contributions to the mechanical properties of the composites were also studied in detail.