Abstract: A carbon fiber network reinforcement (CFNR) was prepared by bonding short carbon fibers with phenol formaldehyde resin followed by carbonization.The CFNR was vacuum-impregnated with molten polypropylene (PP) to produce a CFNR/PP composite with a low thermal expansion coefficient and high stiffness.The microstructure and thermal mechanical properties of the composite were characterized by scanning electron microscopy and thermal mechanical tests.Results show that CFNR is more effective in improving the stiffness and thermal dimensional stability of polymer matrix composites than short carbon fibers.The deformation rate of a conventional short carbon fiber (SCF)/PP composite is 2.3 times higher than that of the CFNR/PP composite under the same load.The decreasing order of the storage and bend moduli is CFNR/PP > SCF/PP > PP.The bend moduli of the CFNR/PP composite at 30 and 110℃ are about 1.8 and 2.5 times that of the SCF/PP composite,respectively.The average thermal expansion coefficient of the CFNR/PP composite between 30 to 120℃ is 25% of that of the SCF/PP composite.