The work aims to modify interfacial defects of diamond/copper composites, inhibit the weak wettability between diamond and copper and enhance the interfacial bonding of composites by adding rare earth neodymium. Spark plasma sintering (SPS) technique was performed to prepare titanium-coated diamond/copper composite with different mass fractions of rare earth Nd. Scanning electron microscopy (SEM) was used to observe the microstructure at the interface. X-ray diffraction and X-ray energy dispersive spectroscopy were used to analyze the structure at the interface, and the dewatering method was performed to test density and relative density of composites. After rare earth Nd was added, Cu5Nd, NdCu2, Cu3Ti and other phases were promoted at the diamond-copper interface. The defects such as the original voids and holes at the interface of diamond/copper composite were filled by Cu5Nd, NdCu2, Cu3Ti and TiC. The density of diamond/copper composite without Nd was 4.589 g/cm3, and the relative density was 81%; After 3wt% Nd was added, the density and relative density of the composites reached 5.569 g/cm3 and 98% respectively. The density was 21% higher than the composite without Nd. With the increase of Nd content, the defects at the diamond-copper interface gradually decreased, and the interface bonding turned better. Rare earth Nd greatly corrects the defects at the interface of Ti coated diamond/copper composite and modifies the interface with poor wettability between diamond and copper. Addition of Nd can make interface between composites bonded more closely.