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Solvent-free nanofluid displays liquid-like function in the absence of solvent at room temperature by grafting organic salts on the surface of materials. In this study, carbon nanotube (CNT) fluid is synthesized by a chemical grafting method for the preparation of CNTs/copper (Cu) composite powder. After hot-pressing and sintering, the CNTs-fluid/Cu composites are further treated by hot rolling to improve their mechanical properties. The microstructure and mechanical properties of the as-obtained composites are systematically characterized by SEM, TEM, FTIR, Raman, rheological analysis, hardness and tensile tests. It is demonstrated that the optimal mechanical properties of the composite can be achieved by adding 0.75 wt.% CNTs nanofluid. The yield and tensile strength of the resultant material are about 397.6 MPa and 517.5 MPa, respectively, which are 282% and 156% higher than that of pure Cu. Meanwhile, its hardness value reaches 152.2 HV, which is increased by 27% and 38% of pure Cu and the unrolled sample, respectively. Such significant property improvement is conjointly contributed by load transfer strengthening, Orowan strengthening, matrix strengthening and thermal mismatch. This study provides a new insight into the interface structure to enhance the mechanical properties of metal matrix composites. Using chemical grafting technology to synthesize carbon nanotube-like fluids, the agglomeration of carbon nanotubes can be inhibited by the repulsive effect of surface grafting. The improved uniform dispersion of carbon nanotubes in the copper matrix enables the composite to achieve synergistic enhancement of strength and hardness. [ABSTRACT FROM AUTHOR]