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The higher requirements are proposed for the thermal stability and impact toughness of drill bits due to the increasingly complex environment of modern oil and coal mining. Polycrystalline diamond composite sheet (PDC) is the core parts of the drill and has a direct impact on the service life of the drill. The PDC always fail in actual working conditions owing to poor thermal stability and fracture. Carbon nanotubes have excellent mechanical properties, chemical stability and thermal stability. Carbon nanotubes are introduced into PCD layer can solve the problems of poor impact toughness and poor thermal stability in PDC. In this study, carbon nanotubes were used as the reinforcing phase and added into PDC. PDC composites were prepared under high pressure and high temperature (5.5 GPa and 1300℃), and the sintering time was 90 s. The effects of carbon nanotubes on mechanical properties and thermal stability of PDC composites were analyzed, the microstructure, element distribution and phase composition of PCD composites were characterized. The results show that the impact toughness of PDC with 1.4 wt% carbon nanotubes increased from 400 J to 550 J, which is 37.5% higher than that of original PDC. The increase of PCD composites impact toughness is attributed to the removal and bridging of carbon nanotubes during crack deflection. The thermal stability of PDC with 1.6 wt% carbon nanotubes increased from 704℃ to 813℃, the friction coefficient decreased from 0.064 to 0.048. The wear ratio reached 159.69×104, which was 59.64×104 higher than that of the original PDC.