The copper based composite powders containing 0.5~2wt.% CNTs were prepared by molecular-level method combined with the two-step mixing process using CNTs, electrolytic Cu powder and Cu (CH₃COO) ₂.H₂O as raw materials, and then the Cu-CNTs composites were prepared by spark plasma sintering. The influence of preparation process and CNTs content on the microstructure, electrical conductivity and mechanical properties of Cu-CNTs composites were studied. The results show that when CNTs content is less than 1.0wt.%, Cu-CNTs composite powders prepared by two-step mixing process have good homogeneity and good dispersibility. The Cu-CNTs composites with high density and uniform CNTs were obtained after sintering. When the content of CNTs is more than 1.0wt.%, the densities and the uniformity of CNTs are obviously decreased. With the increase of the CNTs content, the strength of composites increases in initial stage and then declines, and the plasticity and electrical conductivity tend to decrease. Compared with the high-energy ball milling and molecular level method, the Cu-1.0wt.%CNTs composites prepared by two-step method exhibits the superior mechanical properties, including the electrical conductivity of 51.7 MS/m (89.1% IACS), the hardness of 113 HV, the tensile strength of 279 MPa, and the elongation of 9.3%.