Abstract: The copper-matrix composites reinforced by graphite flake and carbon fiber were prepared by vacuum hot pressing technique. The effects of carbon fiber content on the microstructure, mechanical properties and thermal properties of the composites were discussed. The results show that the prepared graphite flake-carbon fiber/copper matrix composites have good interface bonding. The carbon fibers can be uniformly dispersed in the matrix and the bending strength of the composites can be improved when the volume fraction of 0.5vol%-1.5vol% carbon fibers is added. When the content of carbon fiber is 1.5vol%, the bending strength reaches the maximum of 126 MPa, which is increased by 46% compared with that without carbon fiber. However, the excessive addition of carbon fiber (2vol% or more) leads to an uneven distribution of carbon fiber, and the bending strength of composites decreases. The thermal conductivity of the composite decreases slightly with the addition of carbon fiber, from 549 W/(m·K) to 527 W/(m·K). The acoustic mismatch model (AMM) was used in conjunction with Digimat’s MF module to effectively predict the thermal conductivity of multiphase composites.